Serhiy Storchaka | d7a4415 | 2015-11-12 11:23:04 +0200 | [diff] [blame] | 1 | import copy |
Antoine Pitrou | 796564c | 2013-07-30 19:59:21 +0200 | [diff] [blame] | 2 | import gc |
Serhiy Storchaka | d7a4415 | 2015-11-12 11:23:04 +0200 | [diff] [blame] | 3 | import pickle |
Antoine Pitrou | 796564c | 2013-07-30 19:59:21 +0200 | [diff] [blame] | 4 | import sys |
| 5 | import unittest |
| 6 | import weakref |
Yury Selivanov | e13f8f3 | 2015-07-03 00:23:30 -0400 | [diff] [blame] | 7 | import inspect |
Antoine Pitrou | 796564c | 2013-07-30 19:59:21 +0200 | [diff] [blame] | 8 | |
| 9 | from test import support |
| 10 | |
Isaiah Peng | 4cc3eb4 | 2018-05-16 10:05:17 +0200 | [diff] [blame] | 11 | try: |
| 12 | import _testcapi |
| 13 | except ImportError: |
| 14 | _testcapi = None |
Nathaniel J. Smith | ab4413a | 2017-05-17 13:33:23 -0700 | [diff] [blame] | 15 | |
| 16 | |
| 17 | # This tests to make sure that if a SIGINT arrives just before we send into a |
| 18 | # yield from chain, the KeyboardInterrupt is raised in the innermost |
| 19 | # generator (see bpo-30039). |
Isaiah Peng | 4cc3eb4 | 2018-05-16 10:05:17 +0200 | [diff] [blame] | 20 | @unittest.skipUnless(_testcapi is not None and |
| 21 | hasattr(_testcapi, "raise_SIGINT_then_send_None"), |
| 22 | "needs _testcapi.raise_SIGINT_then_send_None") |
Nathaniel J. Smith | ab4413a | 2017-05-17 13:33:23 -0700 | [diff] [blame] | 23 | class SignalAndYieldFromTest(unittest.TestCase): |
| 24 | |
| 25 | def generator1(self): |
| 26 | return (yield from self.generator2()) |
| 27 | |
| 28 | def generator2(self): |
| 29 | try: |
| 30 | yield |
| 31 | except KeyboardInterrupt: |
| 32 | return "PASSED" |
| 33 | else: |
| 34 | return "FAILED" |
| 35 | |
| 36 | def test_raise_and_yield_from(self): |
| 37 | gen = self.generator1() |
| 38 | gen.send(None) |
| 39 | try: |
| 40 | _testcapi.raise_SIGINT_then_send_None(gen) |
| 41 | except BaseException as _exc: |
| 42 | exc = _exc |
| 43 | self.assertIs(type(exc), StopIteration) |
| 44 | self.assertEqual(exc.value, "PASSED") |
| 45 | |
Antoine Pitrou | 796564c | 2013-07-30 19:59:21 +0200 | [diff] [blame] | 46 | |
| 47 | class FinalizationTest(unittest.TestCase): |
| 48 | |
| 49 | def test_frame_resurrect(self): |
| 50 | # A generator frame can be resurrected by a generator's finalization. |
| 51 | def gen(): |
| 52 | nonlocal frame |
| 53 | try: |
| 54 | yield |
| 55 | finally: |
| 56 | frame = sys._getframe() |
| 57 | |
| 58 | g = gen() |
| 59 | wr = weakref.ref(g) |
| 60 | next(g) |
| 61 | del g |
| 62 | support.gc_collect() |
| 63 | self.assertIs(wr(), None) |
| 64 | self.assertTrue(frame) |
| 65 | del frame |
| 66 | support.gc_collect() |
| 67 | |
| 68 | def test_refcycle(self): |
| 69 | # A generator caught in a refcycle gets finalized anyway. |
| 70 | old_garbage = gc.garbage[:] |
| 71 | finalized = False |
| 72 | def gen(): |
| 73 | nonlocal finalized |
| 74 | try: |
| 75 | g = yield |
| 76 | yield 1 |
| 77 | finally: |
| 78 | finalized = True |
| 79 | |
| 80 | g = gen() |
| 81 | next(g) |
| 82 | g.send(g) |
| 83 | self.assertGreater(sys.getrefcount(g), 2) |
| 84 | self.assertFalse(finalized) |
| 85 | del g |
| 86 | support.gc_collect() |
| 87 | self.assertTrue(finalized) |
| 88 | self.assertEqual(gc.garbage, old_garbage) |
| 89 | |
Serhiy Storchaka | c775ad6 | 2015-03-11 18:20:35 +0200 | [diff] [blame] | 90 | def test_lambda_generator(self): |
| 91 | # Issue #23192: Test that a lambda returning a generator behaves |
| 92 | # like the equivalent function |
| 93 | f = lambda: (yield 1) |
| 94 | def g(): return (yield 1) |
| 95 | |
| 96 | # test 'yield from' |
| 97 | f2 = lambda: (yield from g()) |
| 98 | def g2(): return (yield from g()) |
| 99 | |
| 100 | f3 = lambda: (yield from f()) |
| 101 | def g3(): return (yield from f()) |
| 102 | |
| 103 | for gen_fun in (f, g, f2, g2, f3, g3): |
| 104 | gen = gen_fun() |
| 105 | self.assertEqual(next(gen), 1) |
| 106 | with self.assertRaises(StopIteration) as cm: |
| 107 | gen.send(2) |
| 108 | self.assertEqual(cm.exception.value, 2) |
| 109 | |
Antoine Pitrou | 796564c | 2013-07-30 19:59:21 +0200 | [diff] [blame] | 110 | |
Victor Stinner | 40ee301 | 2014-06-16 15:59:28 +0200 | [diff] [blame] | 111 | class GeneratorTest(unittest.TestCase): |
| 112 | |
| 113 | def test_name(self): |
| 114 | def func(): |
| 115 | yield 1 |
| 116 | |
| 117 | # check generator names |
| 118 | gen = func() |
| 119 | self.assertEqual(gen.__name__, "func") |
| 120 | self.assertEqual(gen.__qualname__, |
| 121 | "GeneratorTest.test_name.<locals>.func") |
| 122 | |
| 123 | # modify generator names |
| 124 | gen.__name__ = "name" |
| 125 | gen.__qualname__ = "qualname" |
| 126 | self.assertEqual(gen.__name__, "name") |
| 127 | self.assertEqual(gen.__qualname__, "qualname") |
| 128 | |
| 129 | # generator names must be a string and cannot be deleted |
| 130 | self.assertRaises(TypeError, setattr, gen, '__name__', 123) |
| 131 | self.assertRaises(TypeError, setattr, gen, '__qualname__', 123) |
| 132 | self.assertRaises(TypeError, delattr, gen, '__name__') |
| 133 | self.assertRaises(TypeError, delattr, gen, '__qualname__') |
| 134 | |
| 135 | # modify names of the function creating the generator |
| 136 | func.__qualname__ = "func_qualname" |
| 137 | func.__name__ = "func_name" |
| 138 | gen = func() |
| 139 | self.assertEqual(gen.__name__, "func_name") |
| 140 | self.assertEqual(gen.__qualname__, "func_qualname") |
| 141 | |
| 142 | # unnamed generator |
| 143 | gen = (x for x in range(10)) |
| 144 | self.assertEqual(gen.__name__, |
| 145 | "<genexpr>") |
| 146 | self.assertEqual(gen.__qualname__, |
| 147 | "GeneratorTest.test_name.<locals>.<genexpr>") |
| 148 | |
Serhiy Storchaka | d7a4415 | 2015-11-12 11:23:04 +0200 | [diff] [blame] | 149 | def test_copy(self): |
| 150 | def f(): |
| 151 | yield 1 |
| 152 | g = f() |
| 153 | with self.assertRaises(TypeError): |
| 154 | copy.copy(g) |
| 155 | |
| 156 | def test_pickle(self): |
| 157 | def f(): |
| 158 | yield 1 |
| 159 | g = f() |
| 160 | for proto in range(pickle.HIGHEST_PROTOCOL + 1): |
| 161 | with self.assertRaises((TypeError, pickle.PicklingError)): |
| 162 | pickle.dumps(g, proto) |
| 163 | |
Victor Stinner | 40ee301 | 2014-06-16 15:59:28 +0200 | [diff] [blame] | 164 | |
Victor Stinner | 26f7b8a | 2015-01-31 10:29:47 +0100 | [diff] [blame] | 165 | class ExceptionTest(unittest.TestCase): |
| 166 | # Tests for the issue #23353: check that the currently handled exception |
| 167 | # is correctly saved/restored in PyEval_EvalFrameEx(). |
| 168 | |
| 169 | def test_except_throw(self): |
| 170 | def store_raise_exc_generator(): |
| 171 | try: |
| 172 | self.assertEqual(sys.exc_info()[0], None) |
| 173 | yield |
| 174 | except Exception as exc: |
| 175 | # exception raised by gen.throw(exc) |
| 176 | self.assertEqual(sys.exc_info()[0], ValueError) |
| 177 | self.assertIsNone(exc.__context__) |
| 178 | yield |
| 179 | |
| 180 | # ensure that the exception is not lost |
| 181 | self.assertEqual(sys.exc_info()[0], ValueError) |
| 182 | yield |
| 183 | |
| 184 | # we should be able to raise back the ValueError |
| 185 | raise |
| 186 | |
| 187 | make = store_raise_exc_generator() |
| 188 | next(make) |
| 189 | |
| 190 | try: |
| 191 | raise ValueError() |
| 192 | except Exception as exc: |
| 193 | try: |
| 194 | make.throw(exc) |
| 195 | except Exception: |
| 196 | pass |
| 197 | |
| 198 | next(make) |
| 199 | with self.assertRaises(ValueError) as cm: |
| 200 | next(make) |
| 201 | self.assertIsNone(cm.exception.__context__) |
| 202 | |
| 203 | self.assertEqual(sys.exc_info(), (None, None, None)) |
| 204 | |
| 205 | def test_except_next(self): |
| 206 | def gen(): |
| 207 | self.assertEqual(sys.exc_info()[0], ValueError) |
| 208 | yield "done" |
| 209 | |
| 210 | g = gen() |
| 211 | try: |
| 212 | raise ValueError |
| 213 | except Exception: |
| 214 | self.assertEqual(next(g), "done") |
| 215 | self.assertEqual(sys.exc_info(), (None, None, None)) |
| 216 | |
| 217 | def test_except_gen_except(self): |
| 218 | def gen(): |
| 219 | try: |
| 220 | self.assertEqual(sys.exc_info()[0], None) |
| 221 | yield |
| 222 | # we are called from "except ValueError:", TypeError must |
| 223 | # inherit ValueError in its context |
| 224 | raise TypeError() |
| 225 | except TypeError as exc: |
| 226 | self.assertEqual(sys.exc_info()[0], TypeError) |
| 227 | self.assertEqual(type(exc.__context__), ValueError) |
| 228 | # here we are still called from the "except ValueError:" |
| 229 | self.assertEqual(sys.exc_info()[0], ValueError) |
| 230 | yield |
| 231 | self.assertIsNone(sys.exc_info()[0]) |
| 232 | yield "done" |
| 233 | |
| 234 | g = gen() |
| 235 | next(g) |
| 236 | try: |
| 237 | raise ValueError |
| 238 | except Exception: |
| 239 | next(g) |
| 240 | |
| 241 | self.assertEqual(next(g), "done") |
| 242 | self.assertEqual(sys.exc_info(), (None, None, None)) |
| 243 | |
| 244 | def test_except_throw_exception_context(self): |
| 245 | def gen(): |
| 246 | try: |
| 247 | try: |
| 248 | self.assertEqual(sys.exc_info()[0], None) |
| 249 | yield |
| 250 | except ValueError: |
| 251 | # we are called from "except ValueError:" |
| 252 | self.assertEqual(sys.exc_info()[0], ValueError) |
| 253 | raise TypeError() |
| 254 | except Exception as exc: |
| 255 | self.assertEqual(sys.exc_info()[0], TypeError) |
| 256 | self.assertEqual(type(exc.__context__), ValueError) |
| 257 | # we are still called from "except ValueError:" |
| 258 | self.assertEqual(sys.exc_info()[0], ValueError) |
| 259 | yield |
| 260 | self.assertIsNone(sys.exc_info()[0]) |
| 261 | yield "done" |
| 262 | |
| 263 | g = gen() |
| 264 | next(g) |
| 265 | try: |
| 266 | raise ValueError |
| 267 | except Exception as exc: |
| 268 | g.throw(exc) |
| 269 | |
| 270 | self.assertEqual(next(g), "done") |
| 271 | self.assertEqual(sys.exc_info(), (None, None, None)) |
| 272 | |
Yury Selivanov | 43c47fe | 2018-01-26 15:24:24 -0500 | [diff] [blame] | 273 | def test_stopiteration_error(self): |
Yury Selivanov | 6833339 | 2015-05-22 11:16:47 -0400 | [diff] [blame] | 274 | # See also PEP 479. |
| 275 | |
| 276 | def gen(): |
| 277 | raise StopIteration |
| 278 | yield |
| 279 | |
Yury Selivanov | 43c47fe | 2018-01-26 15:24:24 -0500 | [diff] [blame] | 280 | with self.assertRaisesRegex(RuntimeError, 'raised StopIteration'): |
Yury Selivanov | 6833339 | 2015-05-22 11:16:47 -0400 | [diff] [blame] | 281 | next(gen()) |
| 282 | |
Yury Selivanov | 6833339 | 2015-05-22 11:16:47 -0400 | [diff] [blame] | 283 | def test_tutorial_stopiteration(self): |
| 284 | # Raise StopIteration" stops the generator too: |
| 285 | |
| 286 | def f(): |
| 287 | yield 1 |
| 288 | raise StopIteration |
| 289 | yield 2 # never reached |
| 290 | |
| 291 | g = f() |
| 292 | self.assertEqual(next(g), 1) |
| 293 | |
Yury Selivanov | 43c47fe | 2018-01-26 15:24:24 -0500 | [diff] [blame] | 294 | with self.assertRaisesRegex(RuntimeError, 'raised StopIteration'): |
Yury Selivanov | 6833339 | 2015-05-22 11:16:47 -0400 | [diff] [blame] | 295 | next(g) |
| 296 | |
Serhiy Storchaka | 24411f8 | 2016-11-06 18:44:42 +0200 | [diff] [blame] | 297 | def test_return_tuple(self): |
| 298 | def g(): |
| 299 | return (yield 1) |
| 300 | |
| 301 | gen = g() |
| 302 | self.assertEqual(next(gen), 1) |
| 303 | with self.assertRaises(StopIteration) as cm: |
| 304 | gen.send((2,)) |
| 305 | self.assertEqual(cm.exception.value, (2,)) |
| 306 | |
| 307 | def test_return_stopiteration(self): |
| 308 | def g(): |
| 309 | return (yield 1) |
| 310 | |
| 311 | gen = g() |
| 312 | self.assertEqual(next(gen), 1) |
| 313 | with self.assertRaises(StopIteration) as cm: |
| 314 | gen.send(StopIteration(2)) |
| 315 | self.assertIsInstance(cm.exception.value, StopIteration) |
| 316 | self.assertEqual(cm.exception.value.value, 2) |
| 317 | |
Victor Stinner | 26f7b8a | 2015-01-31 10:29:47 +0100 | [diff] [blame] | 318 | |
Yury Selivanov | e13f8f3 | 2015-07-03 00:23:30 -0400 | [diff] [blame] | 319 | class YieldFromTests(unittest.TestCase): |
| 320 | def test_generator_gi_yieldfrom(self): |
| 321 | def a(): |
| 322 | self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_RUNNING) |
| 323 | self.assertIsNone(gen_b.gi_yieldfrom) |
| 324 | yield |
| 325 | self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_RUNNING) |
| 326 | self.assertIsNone(gen_b.gi_yieldfrom) |
| 327 | |
| 328 | def b(): |
| 329 | self.assertIsNone(gen_b.gi_yieldfrom) |
| 330 | yield from a() |
| 331 | self.assertIsNone(gen_b.gi_yieldfrom) |
| 332 | yield |
| 333 | self.assertIsNone(gen_b.gi_yieldfrom) |
| 334 | |
| 335 | gen_b = b() |
| 336 | self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_CREATED) |
| 337 | self.assertIsNone(gen_b.gi_yieldfrom) |
| 338 | |
| 339 | gen_b.send(None) |
| 340 | self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_SUSPENDED) |
| 341 | self.assertEqual(gen_b.gi_yieldfrom.gi_code.co_name, 'a') |
| 342 | |
| 343 | gen_b.send(None) |
| 344 | self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_SUSPENDED) |
| 345 | self.assertIsNone(gen_b.gi_yieldfrom) |
| 346 | |
| 347 | [] = gen_b # Exhaust generator |
| 348 | self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_CLOSED) |
| 349 | self.assertIsNone(gen_b.gi_yieldfrom) |
| 350 | |
| 351 | |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 352 | tutorial_tests = """ |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 353 | Let's try a simple generator: |
| 354 | |
| 355 | >>> def f(): |
| 356 | ... yield 1 |
| 357 | ... yield 2 |
| 358 | |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 359 | >>> for i in f(): |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 360 | ... print(i) |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 361 | 1 |
| 362 | 2 |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 363 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 364 | >>> next(g) |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 365 | 1 |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 366 | >>> next(g) |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 367 | 2 |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 368 | |
Tim Peters | 2106ef0 | 2001-06-25 01:30:12 +0000 | [diff] [blame] | 369 | "Falling off the end" stops the generator: |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 370 | |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 371 | >>> next(g) |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 372 | Traceback (most recent call last): |
| 373 | File "<stdin>", line 1, in ? |
| 374 | File "<stdin>", line 2, in g |
| 375 | StopIteration |
| 376 | |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 377 | "return" also stops the generator: |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 378 | |
| 379 | >>> def f(): |
| 380 | ... yield 1 |
| 381 | ... return |
| 382 | ... yield 2 # never reached |
| 383 | ... |
| 384 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 385 | >>> next(g) |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 386 | 1 |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 387 | >>> next(g) |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 388 | Traceback (most recent call last): |
| 389 | File "<stdin>", line 1, in ? |
| 390 | File "<stdin>", line 3, in f |
| 391 | StopIteration |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 392 | >>> next(g) # once stopped, can't be resumed |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 393 | Traceback (most recent call last): |
| 394 | File "<stdin>", line 1, in ? |
| 395 | StopIteration |
| 396 | |
Yury Selivanov | 6833339 | 2015-05-22 11:16:47 -0400 | [diff] [blame] | 397 | However, "return" and StopIteration are not exactly equivalent: |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 398 | |
| 399 | >>> def g1(): |
| 400 | ... try: |
| 401 | ... return |
| 402 | ... except: |
| 403 | ... yield 1 |
| 404 | ... |
| 405 | >>> list(g1()) |
| 406 | [] |
| 407 | |
| 408 | >>> def g2(): |
| 409 | ... try: |
| 410 | ... raise StopIteration |
| 411 | ... except: |
| 412 | ... yield 42 |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 413 | >>> print(list(g2())) |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 414 | [42] |
| 415 | |
| 416 | This may be surprising at first: |
| 417 | |
| 418 | >>> def g3(): |
| 419 | ... try: |
| 420 | ... return |
| 421 | ... finally: |
| 422 | ... yield 1 |
| 423 | ... |
| 424 | >>> list(g3()) |
| 425 | [1] |
| 426 | |
| 427 | Let's create an alternate range() function implemented as a generator: |
| 428 | |
| 429 | >>> def yrange(n): |
| 430 | ... for i in range(n): |
| 431 | ... yield i |
| 432 | ... |
| 433 | >>> list(yrange(5)) |
| 434 | [0, 1, 2, 3, 4] |
| 435 | |
| 436 | Generators always return to the most recent caller: |
| 437 | |
| 438 | >>> def creator(): |
| 439 | ... r = yrange(5) |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 440 | ... print("creator", next(r)) |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 441 | ... return r |
Guido van Rossum | c420b2f | 2007-02-09 22:09:01 +0000 | [diff] [blame] | 442 | ... |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 443 | >>> def caller(): |
| 444 | ... r = creator() |
| 445 | ... for i in r: |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 446 | ... print("caller", i) |
Guido van Rossum | c420b2f | 2007-02-09 22:09:01 +0000 | [diff] [blame] | 447 | ... |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 448 | >>> caller() |
| 449 | creator 0 |
| 450 | caller 1 |
| 451 | caller 2 |
| 452 | caller 3 |
| 453 | caller 4 |
| 454 | |
| 455 | Generators can call other generators: |
| 456 | |
| 457 | >>> def zrange(n): |
| 458 | ... for i in yrange(n): |
| 459 | ... yield i |
| 460 | ... |
| 461 | >>> list(zrange(5)) |
| 462 | [0, 1, 2, 3, 4] |
| 463 | |
| 464 | """ |
| 465 | |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 466 | # The examples from PEP 255. |
| 467 | |
| 468 | pep_tests = """ |
| 469 | |
Tim Peters | e561463 | 2001-08-15 04:41:19 +0000 | [diff] [blame] | 470 | Specification: Yield |
| 471 | |
| 472 | Restriction: A generator cannot be resumed while it is actively |
| 473 | running: |
| 474 | |
| 475 | >>> def g(): |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 476 | ... i = next(me) |
Tim Peters | e561463 | 2001-08-15 04:41:19 +0000 | [diff] [blame] | 477 | ... yield i |
| 478 | >>> me = g() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 479 | >>> next(me) |
Tim Peters | e561463 | 2001-08-15 04:41:19 +0000 | [diff] [blame] | 480 | Traceback (most recent call last): |
| 481 | ... |
| 482 | File "<string>", line 2, in g |
| 483 | ValueError: generator already executing |
| 484 | |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 485 | Specification: Return |
| 486 | |
| 487 | Note that return isn't always equivalent to raising StopIteration: the |
| 488 | difference lies in how enclosing try/except constructs are treated. |
| 489 | For example, |
| 490 | |
| 491 | >>> def f1(): |
| 492 | ... try: |
| 493 | ... return |
| 494 | ... except: |
| 495 | ... yield 1 |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 496 | >>> print(list(f1())) |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 497 | [] |
| 498 | |
| 499 | because, as in any function, return simply exits, but |
| 500 | |
| 501 | >>> def f2(): |
| 502 | ... try: |
| 503 | ... raise StopIteration |
| 504 | ... except: |
| 505 | ... yield 42 |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 506 | >>> print(list(f2())) |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 507 | [42] |
| 508 | |
| 509 | because StopIteration is captured by a bare "except", as is any |
| 510 | exception. |
| 511 | |
| 512 | Specification: Generators and Exception Propagation |
| 513 | |
| 514 | >>> def f(): |
Tim Peters | 3caca23 | 2001-12-06 06:23:26 +0000 | [diff] [blame] | 515 | ... return 1//0 |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 516 | >>> def g(): |
| 517 | ... yield f() # the zero division exception propagates |
| 518 | ... yield 42 # and we'll never get here |
| 519 | >>> k = g() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 520 | >>> next(k) |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 521 | Traceback (most recent call last): |
| 522 | File "<stdin>", line 1, in ? |
| 523 | File "<stdin>", line 2, in g |
| 524 | File "<stdin>", line 2, in f |
| 525 | ZeroDivisionError: integer division or modulo by zero |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 526 | >>> next(k) # and the generator cannot be resumed |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 527 | Traceback (most recent call last): |
| 528 | File "<stdin>", line 1, in ? |
| 529 | StopIteration |
| 530 | >>> |
| 531 | |
| 532 | Specification: Try/Except/Finally |
| 533 | |
| 534 | >>> def f(): |
| 535 | ... try: |
| 536 | ... yield 1 |
| 537 | ... try: |
| 538 | ... yield 2 |
Tim Peters | 3caca23 | 2001-12-06 06:23:26 +0000 | [diff] [blame] | 539 | ... 1//0 |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 540 | ... yield 3 # never get here |
| 541 | ... except ZeroDivisionError: |
| 542 | ... yield 4 |
| 543 | ... yield 5 |
| 544 | ... raise |
| 545 | ... except: |
| 546 | ... yield 6 |
| 547 | ... yield 7 # the "raise" above stops this |
| 548 | ... except: |
| 549 | ... yield 8 |
| 550 | ... yield 9 |
| 551 | ... try: |
| 552 | ... x = 12 |
| 553 | ... finally: |
| 554 | ... yield 10 |
| 555 | ... yield 11 |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 556 | >>> print(list(f())) |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 557 | [1, 2, 4, 5, 8, 9, 10, 11] |
| 558 | >>> |
| 559 | |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 560 | Guido's binary tree example. |
| 561 | |
| 562 | >>> # A binary tree class. |
| 563 | >>> class Tree: |
| 564 | ... |
| 565 | ... def __init__(self, label, left=None, right=None): |
| 566 | ... self.label = label |
| 567 | ... self.left = left |
| 568 | ... self.right = right |
| 569 | ... |
| 570 | ... def __repr__(self, level=0, indent=" "): |
Walter Dörwald | 70a6b49 | 2004-02-12 17:35:32 +0000 | [diff] [blame] | 571 | ... s = level*indent + repr(self.label) |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 572 | ... if self.left: |
| 573 | ... s = s + "\\n" + self.left.__repr__(level+1, indent) |
| 574 | ... if self.right: |
| 575 | ... s = s + "\\n" + self.right.__repr__(level+1, indent) |
| 576 | ... return s |
| 577 | ... |
| 578 | ... def __iter__(self): |
| 579 | ... return inorder(self) |
| 580 | |
| 581 | >>> # Create a Tree from a list. |
| 582 | >>> def tree(list): |
| 583 | ... n = len(list) |
| 584 | ... if n == 0: |
| 585 | ... return [] |
Tim Peters | 3caca23 | 2001-12-06 06:23:26 +0000 | [diff] [blame] | 586 | ... i = n // 2 |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 587 | ... return Tree(list[i], tree(list[:i]), tree(list[i+1:])) |
| 588 | |
| 589 | >>> # Show it off: create a tree. |
| 590 | >>> t = tree("ABCDEFGHIJKLMNOPQRSTUVWXYZ") |
| 591 | |
Tim Peters | d674e17 | 2002-03-10 07:59:13 +0000 | [diff] [blame] | 592 | >>> # A recursive generator that generates Tree labels in in-order. |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 593 | >>> def inorder(t): |
| 594 | ... if t: |
| 595 | ... for x in inorder(t.left): |
| 596 | ... yield x |
| 597 | ... yield t.label |
| 598 | ... for x in inorder(t.right): |
| 599 | ... yield x |
| 600 | |
| 601 | >>> # Show it off: create a tree. |
Edward Loper | 103d26e | 2004-08-09 02:03:30 +0000 | [diff] [blame] | 602 | >>> t = tree("ABCDEFGHIJKLMNOPQRSTUVWXYZ") |
| 603 | >>> # Print the nodes of the tree in in-order. |
| 604 | >>> for x in t: |
Guido van Rossum | c420b2f | 2007-02-09 22:09:01 +0000 | [diff] [blame] | 605 | ... print(' '+x, end='') |
| 606 | A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 607 | |
| 608 | >>> # A non-recursive generator. |
| 609 | >>> def inorder(node): |
| 610 | ... stack = [] |
| 611 | ... while node: |
| 612 | ... while node.left: |
| 613 | ... stack.append(node) |
| 614 | ... node = node.left |
| 615 | ... yield node.label |
| 616 | ... while not node.right: |
| 617 | ... try: |
| 618 | ... node = stack.pop() |
| 619 | ... except IndexError: |
| 620 | ... return |
| 621 | ... yield node.label |
| 622 | ... node = node.right |
| 623 | |
| 624 | >>> # Exercise the non-recursive generator. |
| 625 | >>> for x in t: |
Guido van Rossum | c420b2f | 2007-02-09 22:09:01 +0000 | [diff] [blame] | 626 | ... print(' '+x, end='') |
| 627 | A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 628 | |
| 629 | """ |
| 630 | |
Tim Peters | b2bc6a9 | 2001-06-24 10:14:27 +0000 | [diff] [blame] | 631 | # Examples from Iterator-List and Python-Dev and c.l.py. |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 632 | |
| 633 | email_tests = """ |
| 634 | |
| 635 | The difference between yielding None and returning it. |
| 636 | |
| 637 | >>> def g(): |
| 638 | ... for i in range(3): |
| 639 | ... yield None |
| 640 | ... yield None |
| 641 | ... return |
| 642 | >>> list(g()) |
| 643 | [None, None, None, None] |
| 644 | |
| 645 | Ensure that explicitly raising StopIteration acts like any other exception |
| 646 | in try/except, not like a return. |
| 647 | |
| 648 | >>> def g(): |
| 649 | ... yield 1 |
| 650 | ... try: |
| 651 | ... raise StopIteration |
| 652 | ... except: |
| 653 | ... yield 2 |
| 654 | ... yield 3 |
| 655 | >>> list(g()) |
| 656 | [1, 2, 3] |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 657 | |
Tim Peters | b2bc6a9 | 2001-06-24 10:14:27 +0000 | [diff] [blame] | 658 | Next one was posted to c.l.py. |
| 659 | |
| 660 | >>> def gcomb(x, k): |
| 661 | ... "Generate all combinations of k elements from list x." |
| 662 | ... |
| 663 | ... if k > len(x): |
| 664 | ... return |
| 665 | ... if k == 0: |
| 666 | ... yield [] |
| 667 | ... else: |
| 668 | ... first, rest = x[0], x[1:] |
| 669 | ... # A combination does or doesn't contain first. |
| 670 | ... # If it does, the remainder is a k-1 comb of rest. |
| 671 | ... for c in gcomb(rest, k-1): |
| 672 | ... c.insert(0, first) |
| 673 | ... yield c |
| 674 | ... # If it doesn't contain first, it's a k comb of rest. |
| 675 | ... for c in gcomb(rest, k): |
| 676 | ... yield c |
| 677 | |
Guido van Rossum | 805365e | 2007-05-07 22:24:25 +0000 | [diff] [blame] | 678 | >>> seq = list(range(1, 5)) |
Tim Peters | b2bc6a9 | 2001-06-24 10:14:27 +0000 | [diff] [blame] | 679 | >>> for k in range(len(seq) + 2): |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 680 | ... print("%d-combs of %s:" % (k, seq)) |
Tim Peters | b2bc6a9 | 2001-06-24 10:14:27 +0000 | [diff] [blame] | 681 | ... for c in gcomb(seq, k): |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 682 | ... print(" ", c) |
Tim Peters | b2bc6a9 | 2001-06-24 10:14:27 +0000 | [diff] [blame] | 683 | 0-combs of [1, 2, 3, 4]: |
| 684 | [] |
| 685 | 1-combs of [1, 2, 3, 4]: |
| 686 | [1] |
| 687 | [2] |
| 688 | [3] |
| 689 | [4] |
| 690 | 2-combs of [1, 2, 3, 4]: |
| 691 | [1, 2] |
| 692 | [1, 3] |
| 693 | [1, 4] |
| 694 | [2, 3] |
| 695 | [2, 4] |
| 696 | [3, 4] |
| 697 | 3-combs of [1, 2, 3, 4]: |
| 698 | [1, 2, 3] |
| 699 | [1, 2, 4] |
| 700 | [1, 3, 4] |
| 701 | [2, 3, 4] |
| 702 | 4-combs of [1, 2, 3, 4]: |
| 703 | [1, 2, 3, 4] |
| 704 | 5-combs of [1, 2, 3, 4]: |
Tim Peters | 3e7b1a0 | 2001-06-25 19:46:25 +0000 | [diff] [blame] | 705 | |
Tim Peters | e77f2e2 | 2001-06-26 22:24:51 +0000 | [diff] [blame] | 706 | From the Iterators list, about the types of these things. |
Tim Peters | 3e7b1a0 | 2001-06-25 19:46:25 +0000 | [diff] [blame] | 707 | |
| 708 | >>> def g(): |
| 709 | ... yield 1 |
| 710 | ... |
| 711 | >>> type(g) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 712 | <class 'function'> |
Tim Peters | 3e7b1a0 | 2001-06-25 19:46:25 +0000 | [diff] [blame] | 713 | >>> i = g() |
| 714 | >>> type(i) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 715 | <class 'generator'> |
Tim Peters | 5d2b77c | 2001-09-03 05:47:38 +0000 | [diff] [blame] | 716 | >>> [s for s in dir(i) if not s.startswith('_')] |
Yury Selivanov | e13f8f3 | 2015-07-03 00:23:30 -0400 | [diff] [blame] | 717 | ['close', 'gi_code', 'gi_frame', 'gi_running', 'gi_yieldfrom', 'send', 'throw'] |
Serhiy Storchaka | 9a11f17 | 2013-01-31 16:11:04 +0200 | [diff] [blame] | 718 | >>> from test.support import HAVE_DOCSTRINGS |
Larry Hastings | 581ee36 | 2014-01-28 05:00:08 -0800 | [diff] [blame] | 719 | >>> print(i.__next__.__doc__ if HAVE_DOCSTRINGS else 'Implement next(self).') |
| 720 | Implement next(self). |
Tim Peters | 3e7b1a0 | 2001-06-25 19:46:25 +0000 | [diff] [blame] | 721 | >>> iter(i) is i |
Guido van Rossum | 77f6a65 | 2002-04-03 22:41:51 +0000 | [diff] [blame] | 722 | True |
Tim Peters | 3e7b1a0 | 2001-06-25 19:46:25 +0000 | [diff] [blame] | 723 | >>> import types |
| 724 | >>> isinstance(i, types.GeneratorType) |
Guido van Rossum | 77f6a65 | 2002-04-03 22:41:51 +0000 | [diff] [blame] | 725 | True |
Tim Peters | e77f2e2 | 2001-06-26 22:24:51 +0000 | [diff] [blame] | 726 | |
| 727 | And more, added later. |
| 728 | |
| 729 | >>> i.gi_running |
| 730 | 0 |
| 731 | >>> type(i.gi_frame) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 732 | <class 'frame'> |
Tim Peters | e77f2e2 | 2001-06-26 22:24:51 +0000 | [diff] [blame] | 733 | >>> i.gi_running = 42 |
| 734 | Traceback (most recent call last): |
| 735 | ... |
Collin Winter | 42dae6a | 2007-03-28 21:44:53 +0000 | [diff] [blame] | 736 | AttributeError: readonly attribute |
Tim Peters | e77f2e2 | 2001-06-26 22:24:51 +0000 | [diff] [blame] | 737 | >>> def g(): |
| 738 | ... yield me.gi_running |
| 739 | >>> me = g() |
| 740 | >>> me.gi_running |
| 741 | 0 |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 742 | >>> next(me) |
Tim Peters | e77f2e2 | 2001-06-26 22:24:51 +0000 | [diff] [blame] | 743 | 1 |
| 744 | >>> me.gi_running |
| 745 | 0 |
Tim Peters | 3530266 | 2001-07-02 01:38:33 +0000 | [diff] [blame] | 746 | |
| 747 | A clever union-find implementation from c.l.py, due to David Eppstein. |
| 748 | Sent: Friday, June 29, 2001 12:16 PM |
| 749 | To: python-list@python.org |
| 750 | Subject: Re: PEP 255: Simple Generators |
| 751 | |
| 752 | >>> class disjointSet: |
| 753 | ... def __init__(self, name): |
| 754 | ... self.name = name |
| 755 | ... self.parent = None |
| 756 | ... self.generator = self.generate() |
| 757 | ... |
| 758 | ... def generate(self): |
| 759 | ... while not self.parent: |
| 760 | ... yield self |
| 761 | ... for x in self.parent.generator: |
| 762 | ... yield x |
| 763 | ... |
| 764 | ... def find(self): |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 765 | ... return next(self.generator) |
Tim Peters | 3530266 | 2001-07-02 01:38:33 +0000 | [diff] [blame] | 766 | ... |
| 767 | ... def union(self, parent): |
| 768 | ... if self.parent: |
| 769 | ... raise ValueError("Sorry, I'm not a root!") |
| 770 | ... self.parent = parent |
| 771 | ... |
| 772 | ... def __str__(self): |
| 773 | ... return self.name |
Tim Peters | 3530266 | 2001-07-02 01:38:33 +0000 | [diff] [blame] | 774 | |
| 775 | >>> names = "ABCDEFGHIJKLM" |
| 776 | >>> sets = [disjointSet(name) for name in names] |
| 777 | >>> roots = sets[:] |
| 778 | |
| 779 | >>> import random |
Raymond Hettinger | 28de64f | 2008-01-13 23:40:30 +0000 | [diff] [blame] | 780 | >>> gen = random.Random(42) |
Tim Peters | 3530266 | 2001-07-02 01:38:33 +0000 | [diff] [blame] | 781 | >>> while 1: |
| 782 | ... for s in sets: |
Guido van Rossum | c420b2f | 2007-02-09 22:09:01 +0000 | [diff] [blame] | 783 | ... print(" %s->%s" % (s, s.find()), end='') |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 784 | ... print() |
Tim Peters | 3530266 | 2001-07-02 01:38:33 +0000 | [diff] [blame] | 785 | ... if len(roots) > 1: |
Raymond Hettinger | dd24a9f | 2002-12-30 00:46:09 +0000 | [diff] [blame] | 786 | ... s1 = gen.choice(roots) |
Tim Peters | 3530266 | 2001-07-02 01:38:33 +0000 | [diff] [blame] | 787 | ... roots.remove(s1) |
Raymond Hettinger | dd24a9f | 2002-12-30 00:46:09 +0000 | [diff] [blame] | 788 | ... s2 = gen.choice(roots) |
Tim Peters | 3530266 | 2001-07-02 01:38:33 +0000 | [diff] [blame] | 789 | ... s1.union(s2) |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 790 | ... print("merged", s1, "into", s2) |
Tim Peters | 3530266 | 2001-07-02 01:38:33 +0000 | [diff] [blame] | 791 | ... else: |
| 792 | ... break |
Guido van Rossum | c420b2f | 2007-02-09 22:09:01 +0000 | [diff] [blame] | 793 | A->A B->B C->C D->D E->E F->F G->G H->H I->I J->J K->K L->L M->M |
Raymond Hettinger | c585eec | 2010-09-07 15:00:15 +0000 | [diff] [blame] | 794 | merged K into B |
| 795 | A->A B->B C->C D->D E->E F->F G->G H->H I->I J->J K->B L->L M->M |
Raymond Hettinger | 28de64f | 2008-01-13 23:40:30 +0000 | [diff] [blame] | 796 | merged A into F |
Raymond Hettinger | c585eec | 2010-09-07 15:00:15 +0000 | [diff] [blame] | 797 | A->F B->B C->C D->D E->E F->F G->G H->H I->I J->J K->B L->L M->M |
| 798 | merged E into F |
| 799 | A->F B->B C->C D->D E->F F->F G->G H->H I->I J->J K->B L->L M->M |
| 800 | merged D into C |
| 801 | A->F B->B C->C D->C E->F F->F G->G H->H I->I J->J K->B L->L M->M |
Raymond Hettinger | 28de64f | 2008-01-13 23:40:30 +0000 | [diff] [blame] | 802 | merged M into C |
Raymond Hettinger | c585eec | 2010-09-07 15:00:15 +0000 | [diff] [blame] | 803 | A->F B->B C->C D->C E->F F->F G->G H->H I->I J->J K->B L->L M->C |
| 804 | merged J into B |
| 805 | A->F B->B C->C D->C E->F F->F G->G H->H I->I J->B K->B L->L M->C |
| 806 | merged B into C |
| 807 | A->F B->C C->C D->C E->F F->F G->G H->H I->I J->C K->C L->L M->C |
| 808 | merged F into G |
| 809 | A->G B->C C->C D->C E->G F->G G->G H->H I->I J->C K->C L->L M->C |
| 810 | merged L into C |
| 811 | A->G B->C C->C D->C E->G F->G G->G H->H I->I J->C K->C L->C M->C |
| 812 | merged G into I |
| 813 | A->I B->C C->C D->C E->I F->I G->I H->H I->I J->C K->C L->C M->C |
| 814 | merged I into H |
| 815 | A->H B->C C->C D->C E->H F->H G->H H->H I->H J->C K->C L->C M->C |
| 816 | merged C into H |
| 817 | A->H B->H C->H D->H E->H F->H G->H H->H I->H J->H K->H L->H M->H |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 818 | |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 819 | """ |
Barry Warsaw | 04f357c | 2002-07-23 19:04:11 +0000 | [diff] [blame] | 820 | # Emacs turd ' |
Tim Peters | 6ba5f79 | 2001-06-23 20:45:43 +0000 | [diff] [blame] | 821 | |
Tim Peters | 0f9da0a | 2001-06-23 21:01:47 +0000 | [diff] [blame] | 822 | # Fun tests (for sufficiently warped notions of "fun"). |
| 823 | |
| 824 | fun_tests = """ |
| 825 | |
| 826 | Build up to a recursive Sieve of Eratosthenes generator. |
| 827 | |
| 828 | >>> def firstn(g, n): |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 829 | ... return [next(g) for i in range(n)] |
Tim Peters | 0f9da0a | 2001-06-23 21:01:47 +0000 | [diff] [blame] | 830 | |
| 831 | >>> def intsfrom(i): |
| 832 | ... while 1: |
| 833 | ... yield i |
| 834 | ... i += 1 |
| 835 | |
| 836 | >>> firstn(intsfrom(5), 7) |
| 837 | [5, 6, 7, 8, 9, 10, 11] |
| 838 | |
| 839 | >>> def exclude_multiples(n, ints): |
| 840 | ... for i in ints: |
| 841 | ... if i % n: |
| 842 | ... yield i |
| 843 | |
| 844 | >>> firstn(exclude_multiples(3, intsfrom(1)), 6) |
| 845 | [1, 2, 4, 5, 7, 8] |
| 846 | |
| 847 | >>> def sieve(ints): |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 848 | ... prime = next(ints) |
Tim Peters | 0f9da0a | 2001-06-23 21:01:47 +0000 | [diff] [blame] | 849 | ... yield prime |
| 850 | ... not_divisible_by_prime = exclude_multiples(prime, ints) |
| 851 | ... for p in sieve(not_divisible_by_prime): |
| 852 | ... yield p |
| 853 | |
| 854 | >>> primes = sieve(intsfrom(2)) |
| 855 | >>> firstn(primes, 20) |
| 856 | [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71] |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 857 | |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 858 | |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 859 | Another famous problem: generate all integers of the form |
| 860 | 2**i * 3**j * 5**k |
| 861 | in increasing order, where i,j,k >= 0. Trickier than it may look at first! |
| 862 | Try writing it without generators, and correctly, and without generating |
| 863 | 3 internal results for each result output. |
| 864 | |
| 865 | >>> def times(n, g): |
| 866 | ... for i in g: |
| 867 | ... yield n * i |
| 868 | >>> firstn(times(10, intsfrom(1)), 10) |
| 869 | [10, 20, 30, 40, 50, 60, 70, 80, 90, 100] |
| 870 | |
| 871 | >>> def merge(g, h): |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 872 | ... ng = next(g) |
| 873 | ... nh = next(h) |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 874 | ... while 1: |
| 875 | ... if ng < nh: |
| 876 | ... yield ng |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 877 | ... ng = next(g) |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 878 | ... elif ng > nh: |
| 879 | ... yield nh |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 880 | ... nh = next(h) |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 881 | ... else: |
| 882 | ... yield ng |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 883 | ... ng = next(g) |
| 884 | ... nh = next(h) |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 885 | |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 886 | The following works, but is doing a whale of a lot of redundant work -- |
| 887 | it's not clear how to get the internal uses of m235 to share a single |
| 888 | generator. Note that me_times2 (etc) each need to see every element in the |
| 889 | result sequence. So this is an example where lazy lists are more natural |
| 890 | (you can look at the head of a lazy list any number of times). |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 891 | |
| 892 | >>> def m235(): |
| 893 | ... yield 1 |
| 894 | ... me_times2 = times(2, m235()) |
| 895 | ... me_times3 = times(3, m235()) |
| 896 | ... me_times5 = times(5, m235()) |
| 897 | ... for i in merge(merge(me_times2, |
| 898 | ... me_times3), |
| 899 | ... me_times5): |
| 900 | ... yield i |
| 901 | |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 902 | Don't print "too many" of these -- the implementation above is extremely |
| 903 | inefficient: each call of m235() leads to 3 recursive calls, and in |
| 904 | turn each of those 3 more, and so on, and so on, until we've descended |
| 905 | enough levels to satisfy the print stmts. Very odd: when I printed 5 |
| 906 | lines of results below, this managed to screw up Win98's malloc in "the |
| 907 | usual" way, i.e. the heap grew over 4Mb so Win98 started fragmenting |
| 908 | address space, and it *looked* like a very slow leak. |
| 909 | |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 910 | >>> result = m235() |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 911 | >>> for i in range(3): |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 912 | ... print(firstn(result, 15)) |
Tim Peters | b9e9ff1 | 2001-06-24 03:44:52 +0000 | [diff] [blame] | 913 | [1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24] |
| 914 | [25, 27, 30, 32, 36, 40, 45, 48, 50, 54, 60, 64, 72, 75, 80] |
| 915 | [81, 90, 96, 100, 108, 120, 125, 128, 135, 144, 150, 160, 162, 180, 192] |
Tim Peters | ee30927 | 2001-06-24 05:47:06 +0000 | [diff] [blame] | 916 | |
| 917 | Heh. Here's one way to get a shared list, complete with an excruciating |
| 918 | namespace renaming trick. The *pretty* part is that the times() and merge() |
| 919 | functions can be reused as-is, because they only assume their stream |
| 920 | arguments are iterable -- a LazyList is the same as a generator to times(). |
| 921 | |
| 922 | >>> class LazyList: |
| 923 | ... def __init__(self, g): |
| 924 | ... self.sofar = [] |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 925 | ... self.fetch = g.__next__ |
Tim Peters | ee30927 | 2001-06-24 05:47:06 +0000 | [diff] [blame] | 926 | ... |
| 927 | ... def __getitem__(self, i): |
| 928 | ... sofar, fetch = self.sofar, self.fetch |
| 929 | ... while i >= len(sofar): |
| 930 | ... sofar.append(fetch()) |
| 931 | ... return sofar[i] |
| 932 | |
| 933 | >>> def m235(): |
| 934 | ... yield 1 |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 935 | ... # Gack: m235 below actually refers to a LazyList. |
Tim Peters | ee30927 | 2001-06-24 05:47:06 +0000 | [diff] [blame] | 936 | ... me_times2 = times(2, m235) |
| 937 | ... me_times3 = times(3, m235) |
| 938 | ... me_times5 = times(5, m235) |
| 939 | ... for i in merge(merge(me_times2, |
| 940 | ... me_times3), |
| 941 | ... me_times5): |
| 942 | ... yield i |
| 943 | |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 944 | Print as many of these as you like -- *this* implementation is memory- |
Neil Schemenauer | b20e9db | 2001-07-12 13:26:41 +0000 | [diff] [blame] | 945 | efficient. |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 946 | |
Tim Peters | ee30927 | 2001-06-24 05:47:06 +0000 | [diff] [blame] | 947 | >>> m235 = LazyList(m235()) |
| 948 | >>> for i in range(5): |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 949 | ... print([m235[j] for j in range(15*i, 15*(i+1))]) |
Tim Peters | ee30927 | 2001-06-24 05:47:06 +0000 | [diff] [blame] | 950 | [1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24] |
| 951 | [25, 27, 30, 32, 36, 40, 45, 48, 50, 54, 60, 64, 72, 75, 80] |
| 952 | [81, 90, 96, 100, 108, 120, 125, 128, 135, 144, 150, 160, 162, 180, 192] |
| 953 | [200, 216, 225, 240, 243, 250, 256, 270, 288, 300, 320, 324, 360, 375, 384] |
| 954 | [400, 405, 432, 450, 480, 486, 500, 512, 540, 576, 600, 625, 640, 648, 675] |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 955 | |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 956 | Ye olde Fibonacci generator, LazyList style. |
| 957 | |
| 958 | >>> def fibgen(a, b): |
| 959 | ... |
| 960 | ... def sum(g, h): |
| 961 | ... while 1: |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 962 | ... yield next(g) + next(h) |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 963 | ... |
| 964 | ... def tail(g): |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 965 | ... next(g) # throw first away |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 966 | ... for x in g: |
| 967 | ... yield x |
| 968 | ... |
| 969 | ... yield a |
| 970 | ... yield b |
| 971 | ... for s in sum(iter(fib), |
| 972 | ... tail(iter(fib))): |
| 973 | ... yield s |
| 974 | |
| 975 | >>> fib = LazyList(fibgen(1, 2)) |
| 976 | >>> firstn(iter(fib), 17) |
| 977 | [1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584] |
Georg Brandl | 52715f6 | 2005-08-24 09:02:29 +0000 | [diff] [blame] | 978 | |
| 979 | |
| 980 | Running after your tail with itertools.tee (new in version 2.4) |
| 981 | |
| 982 | The algorithms "m235" (Hamming) and Fibonacci presented above are both |
| 983 | examples of a whole family of FP (functional programming) algorithms |
| 984 | where a function produces and returns a list while the production algorithm |
| 985 | suppose the list as already produced by recursively calling itself. |
| 986 | For these algorithms to work, they must: |
| 987 | |
| 988 | - produce at least a first element without presupposing the existence of |
| 989 | the rest of the list |
| 990 | - produce their elements in a lazy manner |
| 991 | |
| 992 | To work efficiently, the beginning of the list must not be recomputed over |
| 993 | and over again. This is ensured in most FP languages as a built-in feature. |
| 994 | In python, we have to explicitly maintain a list of already computed results |
| 995 | and abandon genuine recursivity. |
| 996 | |
| 997 | This is what had been attempted above with the LazyList class. One problem |
| 998 | with that class is that it keeps a list of all of the generated results and |
| 999 | therefore continually grows. This partially defeats the goal of the generator |
| 1000 | concept, viz. produce the results only as needed instead of producing them |
| 1001 | all and thereby wasting memory. |
| 1002 | |
| 1003 | Thanks to itertools.tee, it is now clear "how to get the internal uses of |
| 1004 | m235 to share a single generator". |
| 1005 | |
| 1006 | >>> from itertools import tee |
| 1007 | >>> def m235(): |
| 1008 | ... def _m235(): |
| 1009 | ... yield 1 |
| 1010 | ... for n in merge(times(2, m2), |
| 1011 | ... merge(times(3, m3), |
| 1012 | ... times(5, m5))): |
| 1013 | ... yield n |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 1014 | ... m1 = _m235() |
| 1015 | ... m2, m3, m5, mRes = tee(m1, 4) |
Georg Brandl | 52715f6 | 2005-08-24 09:02:29 +0000 | [diff] [blame] | 1016 | ... return mRes |
| 1017 | |
| 1018 | >>> it = m235() |
| 1019 | >>> for i in range(5): |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1020 | ... print(firstn(it, 15)) |
Georg Brandl | 52715f6 | 2005-08-24 09:02:29 +0000 | [diff] [blame] | 1021 | [1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24] |
| 1022 | [25, 27, 30, 32, 36, 40, 45, 48, 50, 54, 60, 64, 72, 75, 80] |
| 1023 | [81, 90, 96, 100, 108, 120, 125, 128, 135, 144, 150, 160, 162, 180, 192] |
| 1024 | [200, 216, 225, 240, 243, 250, 256, 270, 288, 300, 320, 324, 360, 375, 384] |
| 1025 | [400, 405, 432, 450, 480, 486, 500, 512, 540, 576, 600, 625, 640, 648, 675] |
| 1026 | |
| 1027 | The "tee" function does just what we want. It internally keeps a generated |
| 1028 | result for as long as it has not been "consumed" from all of the duplicated |
| 1029 | iterators, whereupon it is deleted. You can therefore print the hamming |
| 1030 | sequence during hours without increasing memory usage, or very little. |
| 1031 | |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 1032 | The beauty of it is that recursive running-after-their-tail FP algorithms |
Georg Brandl | 52715f6 | 2005-08-24 09:02:29 +0000 | [diff] [blame] | 1033 | are quite straightforwardly expressed with this Python idiom. |
| 1034 | |
Georg Brandl | 52715f6 | 2005-08-24 09:02:29 +0000 | [diff] [blame] | 1035 | Ye olde Fibonacci generator, tee style. |
| 1036 | |
| 1037 | >>> def fib(): |
Tim Peters | 9e34c04 | 2005-08-26 15:20:46 +0000 | [diff] [blame] | 1038 | ... |
Georg Brandl | 52715f6 | 2005-08-24 09:02:29 +0000 | [diff] [blame] | 1039 | ... def _isum(g, h): |
| 1040 | ... while 1: |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1041 | ... yield next(g) + next(h) |
Tim Peters | 9e34c04 | 2005-08-26 15:20:46 +0000 | [diff] [blame] | 1042 | ... |
Georg Brandl | 52715f6 | 2005-08-24 09:02:29 +0000 | [diff] [blame] | 1043 | ... def _fib(): |
| 1044 | ... yield 1 |
| 1045 | ... yield 2 |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1046 | ... next(fibTail) # throw first away |
Georg Brandl | 52715f6 | 2005-08-24 09:02:29 +0000 | [diff] [blame] | 1047 | ... for res in _isum(fibHead, fibTail): |
| 1048 | ... yield res |
Tim Peters | 9e34c04 | 2005-08-26 15:20:46 +0000 | [diff] [blame] | 1049 | ... |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 1050 | ... realfib = _fib() |
| 1051 | ... fibHead, fibTail, fibRes = tee(realfib, 3) |
Georg Brandl | 52715f6 | 2005-08-24 09:02:29 +0000 | [diff] [blame] | 1052 | ... return fibRes |
| 1053 | |
| 1054 | >>> firstn(fib(), 17) |
| 1055 | [1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584] |
| 1056 | |
Tim Peters | 0f9da0a | 2001-06-23 21:01:47 +0000 | [diff] [blame] | 1057 | """ |
| 1058 | |
Tim Peters | b6c3cea | 2001-06-26 03:36:28 +0000 | [diff] [blame] | 1059 | # syntax_tests mostly provokes SyntaxErrors. Also fiddling with #if 0 |
| 1060 | # hackery. |
Tim Peters | ee30927 | 2001-06-24 05:47:06 +0000 | [diff] [blame] | 1061 | |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1062 | syntax_tests = """ |
| 1063 | |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1064 | These are fine: |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1065 | |
| 1066 | >>> def f(): |
| 1067 | ... yield 1 |
| 1068 | ... return |
| 1069 | |
Tim Peters | aef8cfa | 2004-08-27 15:12:49 +0000 | [diff] [blame] | 1070 | >>> def f(): |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1071 | ... try: |
| 1072 | ... yield 1 |
| 1073 | ... finally: |
| 1074 | ... pass |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1075 | |
Tim Peters | aef8cfa | 2004-08-27 15:12:49 +0000 | [diff] [blame] | 1076 | >>> def f(): |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1077 | ... try: |
| 1078 | ... try: |
Tim Peters | 3caca23 | 2001-12-06 06:23:26 +0000 | [diff] [blame] | 1079 | ... 1//0 |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1080 | ... except ZeroDivisionError: |
Tim Peters | 536cf99 | 2005-12-25 23:18:31 +0000 | [diff] [blame] | 1081 | ... yield 666 |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1082 | ... except: |
| 1083 | ... pass |
| 1084 | ... finally: |
| 1085 | ... pass |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1086 | |
| 1087 | >>> def f(): |
| 1088 | ... try: |
| 1089 | ... try: |
| 1090 | ... yield 12 |
Tim Peters | 3caca23 | 2001-12-06 06:23:26 +0000 | [diff] [blame] | 1091 | ... 1//0 |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1092 | ... except ZeroDivisionError: |
| 1093 | ... yield 666 |
| 1094 | ... except: |
| 1095 | ... try: |
| 1096 | ... x = 12 |
| 1097 | ... finally: |
| 1098 | ... yield 12 |
| 1099 | ... except: |
| 1100 | ... return |
| 1101 | >>> list(f()) |
| 1102 | [12, 666] |
Tim Peters | b6c3cea | 2001-06-26 03:36:28 +0000 | [diff] [blame] | 1103 | |
| 1104 | >>> def f(): |
Tim Peters | 08a898f | 2001-06-28 01:52:22 +0000 | [diff] [blame] | 1105 | ... yield |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1106 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 1107 | <class 'generator'> |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1108 | |
Tim Peters | 08a898f | 2001-06-28 01:52:22 +0000 | [diff] [blame] | 1109 | |
| 1110 | >>> def f(): |
| 1111 | ... if 0: |
| 1112 | ... yield |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1113 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 1114 | <class 'generator'> |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1115 | |
Tim Peters | 08a898f | 2001-06-28 01:52:22 +0000 | [diff] [blame] | 1116 | |
| 1117 | >>> def f(): |
Tim Peters | b6c3cea | 2001-06-26 03:36:28 +0000 | [diff] [blame] | 1118 | ... if 0: |
| 1119 | ... yield 1 |
| 1120 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 1121 | <class 'generator'> |
Tim Peters | b6c3cea | 2001-06-26 03:36:28 +0000 | [diff] [blame] | 1122 | |
| 1123 | >>> def f(): |
| 1124 | ... if "": |
| 1125 | ... yield None |
| 1126 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 1127 | <class 'generator'> |
Tim Peters | b6c3cea | 2001-06-26 03:36:28 +0000 | [diff] [blame] | 1128 | |
| 1129 | >>> def f(): |
| 1130 | ... return |
| 1131 | ... try: |
| 1132 | ... if x==4: |
| 1133 | ... pass |
| 1134 | ... elif 0: |
| 1135 | ... try: |
Tim Peters | 3caca23 | 2001-12-06 06:23:26 +0000 | [diff] [blame] | 1136 | ... 1//0 |
Tim Peters | b6c3cea | 2001-06-26 03:36:28 +0000 | [diff] [blame] | 1137 | ... except SyntaxError: |
| 1138 | ... pass |
| 1139 | ... else: |
| 1140 | ... if 0: |
| 1141 | ... while 12: |
| 1142 | ... x += 1 |
| 1143 | ... yield 2 # don't blink |
| 1144 | ... f(a, b, c, d, e) |
| 1145 | ... else: |
| 1146 | ... pass |
| 1147 | ... except: |
| 1148 | ... x = 1 |
| 1149 | ... return |
| 1150 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 1151 | <class 'generator'> |
Tim Peters | b6c3cea | 2001-06-26 03:36:28 +0000 | [diff] [blame] | 1152 | |
| 1153 | >>> def f(): |
| 1154 | ... if 0: |
| 1155 | ... def g(): |
| 1156 | ... yield 1 |
| 1157 | ... |
| 1158 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 1159 | <class 'NoneType'> |
Tim Peters | b6c3cea | 2001-06-26 03:36:28 +0000 | [diff] [blame] | 1160 | |
| 1161 | >>> def f(): |
| 1162 | ... if 0: |
| 1163 | ... class C: |
| 1164 | ... def __init__(self): |
| 1165 | ... yield 1 |
| 1166 | ... def f(self): |
| 1167 | ... yield 2 |
| 1168 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 1169 | <class 'NoneType'> |
Tim Peters | 08a898f | 2001-06-28 01:52:22 +0000 | [diff] [blame] | 1170 | |
| 1171 | >>> def f(): |
| 1172 | ... if 0: |
| 1173 | ... return |
| 1174 | ... if 0: |
| 1175 | ... yield 2 |
| 1176 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 1177 | <class 'generator'> |
Tim Peters | 08a898f | 2001-06-28 01:52:22 +0000 | [diff] [blame] | 1178 | |
Guido van Rossum | c5fe5eb | 2002-06-12 03:45:21 +0000 | [diff] [blame] | 1179 | This one caused a crash (see SF bug 567538): |
| 1180 | |
| 1181 | >>> def f(): |
| 1182 | ... for i in range(3): |
| 1183 | ... try: |
| 1184 | ... continue |
| 1185 | ... finally: |
| 1186 | ... yield i |
Tim Peters | c411dba | 2002-07-16 21:35:23 +0000 | [diff] [blame] | 1187 | ... |
Guido van Rossum | c5fe5eb | 2002-06-12 03:45:21 +0000 | [diff] [blame] | 1188 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1189 | >>> print(next(g)) |
Guido van Rossum | c5fe5eb | 2002-06-12 03:45:21 +0000 | [diff] [blame] | 1190 | 0 |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1191 | >>> print(next(g)) |
Guido van Rossum | c5fe5eb | 2002-06-12 03:45:21 +0000 | [diff] [blame] | 1192 | 1 |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1193 | >>> print(next(g)) |
Guido van Rossum | c5fe5eb | 2002-06-12 03:45:21 +0000 | [diff] [blame] | 1194 | 2 |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1195 | >>> print(next(g)) |
Guido van Rossum | c5fe5eb | 2002-06-12 03:45:21 +0000 | [diff] [blame] | 1196 | Traceback (most recent call last): |
| 1197 | StopIteration |
Christian Heimes | af98da1 | 2008-01-27 15:18:18 +0000 | [diff] [blame] | 1198 | |
| 1199 | |
| 1200 | Test the gi_code attribute |
| 1201 | |
| 1202 | >>> def f(): |
| 1203 | ... yield 5 |
| 1204 | ... |
| 1205 | >>> g = f() |
| 1206 | >>> g.gi_code is f.__code__ |
| 1207 | True |
| 1208 | >>> next(g) |
| 1209 | 5 |
| 1210 | >>> next(g) |
| 1211 | Traceback (most recent call last): |
| 1212 | StopIteration |
| 1213 | >>> g.gi_code is f.__code__ |
| 1214 | True |
| 1215 | |
Alexandre Vassalotti | e9f305f | 2008-05-16 04:39:54 +0000 | [diff] [blame] | 1216 | |
| 1217 | Test the __name__ attribute and the repr() |
| 1218 | |
| 1219 | >>> def f(): |
| 1220 | ... yield 5 |
| 1221 | ... |
| 1222 | >>> g = f() |
| 1223 | >>> g.__name__ |
| 1224 | 'f' |
| 1225 | >>> repr(g) # doctest: +ELLIPSIS |
Alexandre Vassalotti | bee3253 | 2008-05-16 18:15:12 +0000 | [diff] [blame] | 1226 | '<generator object f at ...>' |
Benjamin Peterson | 371ccfb | 2008-12-27 19:03:36 +0000 | [diff] [blame] | 1227 | |
| 1228 | Lambdas shouldn't have their usual return behavior. |
| 1229 | |
| 1230 | >>> x = lambda: (yield 1) |
| 1231 | >>> list(x()) |
| 1232 | [1] |
| 1233 | |
| 1234 | >>> x = lambda: ((yield 1), (yield 2)) |
| 1235 | >>> list(x()) |
| 1236 | [1, 2] |
Tim Peters | ea2e97a | 2001-06-24 07:10:02 +0000 | [diff] [blame] | 1237 | """ |
| 1238 | |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1239 | # conjoin is a simple backtracking generator, named in honor of Icon's |
| 1240 | # "conjunction" control structure. Pass a list of no-argument functions |
| 1241 | # that return iterable objects. Easiest to explain by example: assume the |
| 1242 | # function list [x, y, z] is passed. Then conjoin acts like: |
| 1243 | # |
| 1244 | # def g(): |
| 1245 | # values = [None] * 3 |
| 1246 | # for values[0] in x(): |
| 1247 | # for values[1] in y(): |
| 1248 | # for values[2] in z(): |
| 1249 | # yield values |
| 1250 | # |
| 1251 | # So some 3-lists of values *may* be generated, each time we successfully |
| 1252 | # get into the innermost loop. If an iterator fails (is exhausted) before |
| 1253 | # then, it "backtracks" to get the next value from the nearest enclosing |
| 1254 | # iterator (the one "to the left"), and starts all over again at the next |
| 1255 | # slot (pumps a fresh iterator). Of course this is most useful when the |
| 1256 | # iterators have side-effects, so that which values *can* be generated at |
| 1257 | # each slot depend on the values iterated at previous slots. |
| 1258 | |
Benjamin Peterson | 78565b2 | 2009-06-28 19:19:51 +0000 | [diff] [blame] | 1259 | def simple_conjoin(gs): |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1260 | |
| 1261 | values = [None] * len(gs) |
| 1262 | |
Benjamin Peterson | 78565b2 | 2009-06-28 19:19:51 +0000 | [diff] [blame] | 1263 | def gen(i): |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1264 | if i >= len(gs): |
| 1265 | yield values |
| 1266 | else: |
| 1267 | for values[i] in gs[i](): |
| 1268 | for x in gen(i+1): |
| 1269 | yield x |
| 1270 | |
| 1271 | for x in gen(0): |
| 1272 | yield x |
| 1273 | |
Tim Peters | c468fd2 | 2001-06-30 07:29:44 +0000 | [diff] [blame] | 1274 | # That works fine, but recursing a level and checking i against len(gs) for |
| 1275 | # each item produced is inefficient. By doing manual loop unrolling across |
| 1276 | # generator boundaries, it's possible to eliminate most of that overhead. |
| 1277 | # This isn't worth the bother *in general* for generators, but conjoin() is |
| 1278 | # a core building block for some CPU-intensive generator applications. |
| 1279 | |
| 1280 | def conjoin(gs): |
| 1281 | |
| 1282 | n = len(gs) |
| 1283 | values = [None] * n |
| 1284 | |
| 1285 | # Do one loop nest at time recursively, until the # of loop nests |
| 1286 | # remaining is divisible by 3. |
| 1287 | |
Benjamin Peterson | 78565b2 | 2009-06-28 19:19:51 +0000 | [diff] [blame] | 1288 | def gen(i): |
Tim Peters | c468fd2 | 2001-06-30 07:29:44 +0000 | [diff] [blame] | 1289 | if i >= n: |
| 1290 | yield values |
| 1291 | |
| 1292 | elif (n-i) % 3: |
| 1293 | ip1 = i+1 |
| 1294 | for values[i] in gs[i](): |
| 1295 | for x in gen(ip1): |
| 1296 | yield x |
| 1297 | |
| 1298 | else: |
| 1299 | for x in _gen3(i): |
| 1300 | yield x |
| 1301 | |
| 1302 | # Do three loop nests at a time, recursing only if at least three more |
| 1303 | # remain. Don't call directly: this is an internal optimization for |
| 1304 | # gen's use. |
| 1305 | |
Benjamin Peterson | 78565b2 | 2009-06-28 19:19:51 +0000 | [diff] [blame] | 1306 | def _gen3(i): |
Tim Peters | c468fd2 | 2001-06-30 07:29:44 +0000 | [diff] [blame] | 1307 | assert i < n and (n-i) % 3 == 0 |
| 1308 | ip1, ip2, ip3 = i+1, i+2, i+3 |
| 1309 | g, g1, g2 = gs[i : ip3] |
| 1310 | |
| 1311 | if ip3 >= n: |
| 1312 | # These are the last three, so we can yield values directly. |
| 1313 | for values[i] in g(): |
| 1314 | for values[ip1] in g1(): |
| 1315 | for values[ip2] in g2(): |
| 1316 | yield values |
| 1317 | |
| 1318 | else: |
| 1319 | # At least 6 loop nests remain; peel off 3 and recurse for the |
| 1320 | # rest. |
| 1321 | for values[i] in g(): |
| 1322 | for values[ip1] in g1(): |
| 1323 | for values[ip2] in g2(): |
| 1324 | for x in _gen3(ip3): |
| 1325 | yield x |
| 1326 | |
| 1327 | for x in gen(0): |
| 1328 | yield x |
| 1329 | |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1330 | # And one more approach: For backtracking apps like the Knight's Tour |
| 1331 | # solver below, the number of backtracking levels can be enormous (one |
| 1332 | # level per square, for the Knight's Tour, so that e.g. a 100x100 board |
| 1333 | # needs 10,000 levels). In such cases Python is likely to run out of |
| 1334 | # stack space due to recursion. So here's a recursion-free version of |
| 1335 | # conjoin too. |
| 1336 | # NOTE WELL: This allows large problems to be solved with only trivial |
| 1337 | # demands on stack space. Without explicitly resumable generators, this is |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1338 | # much harder to achieve. OTOH, this is much slower (up to a factor of 2) |
| 1339 | # than the fancy unrolled recursive conjoin. |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1340 | |
| 1341 | def flat_conjoin(gs): # rename to conjoin to run tests with this instead |
| 1342 | n = len(gs) |
| 1343 | values = [None] * n |
| 1344 | iters = [None] * n |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1345 | _StopIteration = StopIteration # make local because caught a *lot* |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1346 | i = 0 |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1347 | while 1: |
| 1348 | # Descend. |
| 1349 | try: |
| 1350 | while i < n: |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1351 | it = iters[i] = gs[i]().__next__ |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1352 | values[i] = it() |
| 1353 | i += 1 |
| 1354 | except _StopIteration: |
| 1355 | pass |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1356 | else: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1357 | assert i == n |
| 1358 | yield values |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1359 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1360 | # Backtrack until an older iterator can be resumed. |
| 1361 | i -= 1 |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1362 | while i >= 0: |
| 1363 | try: |
| 1364 | values[i] = iters[i]() |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1365 | # Success! Start fresh at next level. |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1366 | i += 1 |
| 1367 | break |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1368 | except _StopIteration: |
| 1369 | # Continue backtracking. |
| 1370 | i -= 1 |
| 1371 | else: |
| 1372 | assert i < 0 |
| 1373 | break |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1374 | |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1375 | # A conjoin-based N-Queens solver. |
| 1376 | |
| 1377 | class Queens: |
| 1378 | def __init__(self, n): |
| 1379 | self.n = n |
| 1380 | rangen = range(n) |
| 1381 | |
| 1382 | # Assign a unique int to each column and diagonal. |
| 1383 | # columns: n of those, range(n). |
| 1384 | # NW-SE diagonals: 2n-1 of these, i-j unique and invariant along |
| 1385 | # each, smallest i-j is 0-(n-1) = 1-n, so add n-1 to shift to 0- |
| 1386 | # based. |
| 1387 | # NE-SW diagonals: 2n-1 of these, i+j unique and invariant along |
| 1388 | # each, smallest i+j is 0, largest is 2n-2. |
| 1389 | |
| 1390 | # For each square, compute a bit vector of the columns and |
| 1391 | # diagonals it covers, and for each row compute a function that |
Martin Panter | 46f5072 | 2016-05-26 05:35:26 +0000 | [diff] [blame] | 1392 | # generates the possibilities for the columns in that row. |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1393 | self.rowgenerators = [] |
| 1394 | for i in rangen: |
Guido van Rossum | e2a383d | 2007-01-15 16:59:06 +0000 | [diff] [blame] | 1395 | rowuses = [(1 << j) | # column ordinal |
| 1396 | (1 << (n + i-j + n-1)) | # NW-SE ordinal |
| 1397 | (1 << (n + 2*n-1 + i+j)) # NE-SW ordinal |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1398 | for j in rangen] |
| 1399 | |
| 1400 | def rowgen(rowuses=rowuses): |
| 1401 | for j in rangen: |
| 1402 | uses = rowuses[j] |
Tim Peters | c468fd2 | 2001-06-30 07:29:44 +0000 | [diff] [blame] | 1403 | if uses & self.used == 0: |
| 1404 | self.used |= uses |
| 1405 | yield j |
| 1406 | self.used &= ~uses |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1407 | |
| 1408 | self.rowgenerators.append(rowgen) |
| 1409 | |
| 1410 | # Generate solutions. |
| 1411 | def solve(self): |
| 1412 | self.used = 0 |
| 1413 | for row2col in conjoin(self.rowgenerators): |
| 1414 | yield row2col |
| 1415 | |
| 1416 | def printsolution(self, row2col): |
| 1417 | n = self.n |
| 1418 | assert n == len(row2col) |
| 1419 | sep = "+" + "-+" * n |
Guido van Rossum | be19ed7 | 2007-02-09 05:37:30 +0000 | [diff] [blame] | 1420 | print(sep) |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1421 | for i in range(n): |
| 1422 | squares = [" " for j in range(n)] |
| 1423 | squares[row2col[i]] = "Q" |
Guido van Rossum | be19ed7 | 2007-02-09 05:37:30 +0000 | [diff] [blame] | 1424 | print("|" + "|".join(squares) + "|") |
| 1425 | print(sep) |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1426 | |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1427 | # A conjoin-based Knight's Tour solver. This is pretty sophisticated |
| 1428 | # (e.g., when used with flat_conjoin above, and passing hard=1 to the |
| 1429 | # constructor, a 200x200 Knight's Tour was found quickly -- note that we're |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1430 | # creating 10s of thousands of generators then!), and is lengthy. |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1431 | |
| 1432 | class Knights: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1433 | def __init__(self, m, n, hard=0): |
| 1434 | self.m, self.n = m, n |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1435 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1436 | # solve() will set up succs[i] to be a list of square #i's |
| 1437 | # successors. |
| 1438 | succs = self.succs = [] |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1439 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1440 | # Remove i0 from each of its successor's successor lists, i.e. |
| 1441 | # successors can't go back to i0 again. Return 0 if we can |
| 1442 | # detect this makes a solution impossible, else return 1. |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1443 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1444 | def remove_from_successors(i0, len=len): |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1445 | # If we remove all exits from a free square, we're dead: |
| 1446 | # even if we move to it next, we can't leave it again. |
| 1447 | # If we create a square with one exit, we must visit it next; |
| 1448 | # else somebody else will have to visit it, and since there's |
| 1449 | # only one adjacent, there won't be a way to leave it again. |
Mike | 53f7a7c | 2017-12-14 14:04:53 +0300 | [diff] [blame] | 1450 | # Finally, if we create more than one free square with a |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1451 | # single exit, we can only move to one of them next, leaving |
| 1452 | # the other one a dead end. |
| 1453 | ne0 = ne1 = 0 |
| 1454 | for i in succs[i0]: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1455 | s = succs[i] |
| 1456 | s.remove(i0) |
| 1457 | e = len(s) |
| 1458 | if e == 0: |
| 1459 | ne0 += 1 |
| 1460 | elif e == 1: |
| 1461 | ne1 += 1 |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1462 | return ne0 == 0 and ne1 < 2 |
| 1463 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1464 | # Put i0 back in each of its successor's successor lists. |
| 1465 | |
| 1466 | def add_to_successors(i0): |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1467 | for i in succs[i0]: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1468 | succs[i].append(i0) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1469 | |
| 1470 | # Generate the first move. |
| 1471 | def first(): |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1472 | if m < 1 or n < 1: |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1473 | return |
| 1474 | |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1475 | # Since we're looking for a cycle, it doesn't matter where we |
| 1476 | # start. Starting in a corner makes the 2nd move easy. |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1477 | corner = self.coords2index(0, 0) |
| 1478 | remove_from_successors(corner) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1479 | self.lastij = corner |
| 1480 | yield corner |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1481 | add_to_successors(corner) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1482 | |
| 1483 | # Generate the second moves. |
| 1484 | def second(): |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1485 | corner = self.coords2index(0, 0) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1486 | assert self.lastij == corner # i.e., we started in the corner |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1487 | if m < 3 or n < 3: |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1488 | return |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1489 | assert len(succs[corner]) == 2 |
| 1490 | assert self.coords2index(1, 2) in succs[corner] |
| 1491 | assert self.coords2index(2, 1) in succs[corner] |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1492 | # Only two choices. Whichever we pick, the other must be the |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1493 | # square picked on move m*n, as it's the only way to get back |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1494 | # to (0, 0). Save its index in self.final so that moves before |
| 1495 | # the last know it must be kept free. |
| 1496 | for i, j in (1, 2), (2, 1): |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1497 | this = self.coords2index(i, j) |
| 1498 | final = self.coords2index(3-i, 3-j) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1499 | self.final = final |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1500 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1501 | remove_from_successors(this) |
| 1502 | succs[final].append(corner) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1503 | self.lastij = this |
| 1504 | yield this |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1505 | succs[final].remove(corner) |
| 1506 | add_to_successors(this) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1507 | |
Leo Arias | c3d9508 | 2018-02-03 18:36:10 -0600 | [diff] [blame] | 1508 | # Generate moves 3 through m*n-1. |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1509 | def advance(len=len): |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1510 | # If some successor has only one exit, must take it. |
| 1511 | # Else favor successors with fewer exits. |
| 1512 | candidates = [] |
| 1513 | for i in succs[self.lastij]: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1514 | e = len(succs[i]) |
| 1515 | assert e > 0, "else remove_from_successors() pruning flawed" |
| 1516 | if e == 1: |
| 1517 | candidates = [(e, i)] |
| 1518 | break |
| 1519 | candidates.append((e, i)) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1520 | else: |
| 1521 | candidates.sort() |
| 1522 | |
| 1523 | for e, i in candidates: |
| 1524 | if i != self.final: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1525 | if remove_from_successors(i): |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1526 | self.lastij = i |
| 1527 | yield i |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1528 | add_to_successors(i) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1529 | |
Leo Arias | c3d9508 | 2018-02-03 18:36:10 -0600 | [diff] [blame] | 1530 | # Generate moves 3 through m*n-1. Alternative version using a |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1531 | # stronger (but more expensive) heuristic to order successors. |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1532 | # Since the # of backtracking levels is m*n, a poor move early on |
| 1533 | # can take eons to undo. Smallest square board for which this |
| 1534 | # matters a lot is 52x52. |
| 1535 | def advance_hard(vmid=(m-1)/2.0, hmid=(n-1)/2.0, len=len): |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1536 | # If some successor has only one exit, must take it. |
| 1537 | # Else favor successors with fewer exits. |
| 1538 | # Break ties via max distance from board centerpoint (favor |
| 1539 | # corners and edges whenever possible). |
| 1540 | candidates = [] |
| 1541 | for i in succs[self.lastij]: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1542 | e = len(succs[i]) |
| 1543 | assert e > 0, "else remove_from_successors() pruning flawed" |
| 1544 | if e == 1: |
| 1545 | candidates = [(e, 0, i)] |
| 1546 | break |
| 1547 | i1, j1 = self.index2coords(i) |
| 1548 | d = (i1 - vmid)**2 + (j1 - hmid)**2 |
| 1549 | candidates.append((e, -d, i)) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1550 | else: |
| 1551 | candidates.sort() |
| 1552 | |
| 1553 | for e, d, i in candidates: |
| 1554 | if i != self.final: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1555 | if remove_from_successors(i): |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1556 | self.lastij = i |
| 1557 | yield i |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1558 | add_to_successors(i) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1559 | |
| 1560 | # Generate the last move. |
| 1561 | def last(): |
| 1562 | assert self.final in succs[self.lastij] |
| 1563 | yield self.final |
| 1564 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1565 | if m*n < 4: |
| 1566 | self.squaregenerators = [first] |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1567 | else: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1568 | self.squaregenerators = [first, second] + \ |
| 1569 | [hard and advance_hard or advance] * (m*n - 3) + \ |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1570 | [last] |
| 1571 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1572 | def coords2index(self, i, j): |
| 1573 | assert 0 <= i < self.m |
| 1574 | assert 0 <= j < self.n |
| 1575 | return i * self.n + j |
| 1576 | |
| 1577 | def index2coords(self, index): |
| 1578 | assert 0 <= index < self.m * self.n |
| 1579 | return divmod(index, self.n) |
| 1580 | |
| 1581 | def _init_board(self): |
| 1582 | succs = self.succs |
| 1583 | del succs[:] |
| 1584 | m, n = self.m, self.n |
| 1585 | c2i = self.coords2index |
| 1586 | |
| 1587 | offsets = [( 1, 2), ( 2, 1), ( 2, -1), ( 1, -2), |
| 1588 | (-1, -2), (-2, -1), (-2, 1), (-1, 2)] |
| 1589 | rangen = range(n) |
| 1590 | for i in range(m): |
| 1591 | for j in rangen: |
| 1592 | s = [c2i(i+io, j+jo) for io, jo in offsets |
| 1593 | if 0 <= i+io < m and |
| 1594 | 0 <= j+jo < n] |
| 1595 | succs.append(s) |
| 1596 | |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1597 | # Generate solutions. |
| 1598 | def solve(self): |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1599 | self._init_board() |
| 1600 | for x in conjoin(self.squaregenerators): |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1601 | yield x |
| 1602 | |
| 1603 | def printsolution(self, x): |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1604 | m, n = self.m, self.n |
| 1605 | assert len(x) == m*n |
| 1606 | w = len(str(m*n)) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1607 | format = "%" + str(w) + "d" |
| 1608 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1609 | squares = [[None] * n for i in range(m)] |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1610 | k = 1 |
| 1611 | for i in x: |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1612 | i1, j1 = self.index2coords(i) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1613 | squares[i1][j1] = format % k |
| 1614 | k += 1 |
| 1615 | |
| 1616 | sep = "+" + ("-" * w + "+") * n |
Guido van Rossum | be19ed7 | 2007-02-09 05:37:30 +0000 | [diff] [blame] | 1617 | print(sep) |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1618 | for i in range(m): |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1619 | row = squares[i] |
Guido van Rossum | be19ed7 | 2007-02-09 05:37:30 +0000 | [diff] [blame] | 1620 | print("|" + "|".join(row) + "|") |
| 1621 | print(sep) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1622 | |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1623 | conjoin_tests = """ |
| 1624 | |
| 1625 | Generate the 3-bit binary numbers in order. This illustrates dumbest- |
| 1626 | possible use of conjoin, just to generate the full cross-product. |
| 1627 | |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1628 | >>> for c in conjoin([lambda: iter((0, 1))] * 3): |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1629 | ... print(c) |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1630 | [0, 0, 0] |
| 1631 | [0, 0, 1] |
| 1632 | [0, 1, 0] |
| 1633 | [0, 1, 1] |
| 1634 | [1, 0, 0] |
| 1635 | [1, 0, 1] |
| 1636 | [1, 1, 0] |
| 1637 | [1, 1, 1] |
| 1638 | |
Tim Peters | c468fd2 | 2001-06-30 07:29:44 +0000 | [diff] [blame] | 1639 | For efficiency in typical backtracking apps, conjoin() yields the same list |
| 1640 | object each time. So if you want to save away a full account of its |
| 1641 | generated sequence, you need to copy its results. |
| 1642 | |
| 1643 | >>> def gencopy(iterator): |
| 1644 | ... for x in iterator: |
| 1645 | ... yield x[:] |
| 1646 | |
| 1647 | >>> for n in range(10): |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1648 | ... all = list(gencopy(conjoin([lambda: iter((0, 1))] * n))) |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1649 | ... print(n, len(all), all[0] == [0] * n, all[-1] == [1] * n) |
Guido van Rossum | 77f6a65 | 2002-04-03 22:41:51 +0000 | [diff] [blame] | 1650 | 0 1 True True |
| 1651 | 1 2 True True |
| 1652 | 2 4 True True |
| 1653 | 3 8 True True |
| 1654 | 4 16 True True |
| 1655 | 5 32 True True |
| 1656 | 6 64 True True |
| 1657 | 7 128 True True |
| 1658 | 8 256 True True |
| 1659 | 9 512 True True |
Tim Peters | c468fd2 | 2001-06-30 07:29:44 +0000 | [diff] [blame] | 1660 | |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1661 | And run an 8-queens solver. |
| 1662 | |
| 1663 | >>> q = Queens(8) |
| 1664 | >>> LIMIT = 2 |
| 1665 | >>> count = 0 |
| 1666 | >>> for row2col in q.solve(): |
| 1667 | ... count += 1 |
| 1668 | ... if count <= LIMIT: |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1669 | ... print("Solution", count) |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1670 | ... q.printsolution(row2col) |
| 1671 | Solution 1 |
| 1672 | +-+-+-+-+-+-+-+-+ |
| 1673 | |Q| | | | | | | | |
| 1674 | +-+-+-+-+-+-+-+-+ |
| 1675 | | | | | |Q| | | | |
| 1676 | +-+-+-+-+-+-+-+-+ |
| 1677 | | | | | | | | |Q| |
| 1678 | +-+-+-+-+-+-+-+-+ |
| 1679 | | | | | | |Q| | | |
| 1680 | +-+-+-+-+-+-+-+-+ |
| 1681 | | | |Q| | | | | | |
| 1682 | +-+-+-+-+-+-+-+-+ |
| 1683 | | | | | | | |Q| | |
| 1684 | +-+-+-+-+-+-+-+-+ |
| 1685 | | |Q| | | | | | | |
| 1686 | +-+-+-+-+-+-+-+-+ |
| 1687 | | | | |Q| | | | | |
| 1688 | +-+-+-+-+-+-+-+-+ |
| 1689 | Solution 2 |
| 1690 | +-+-+-+-+-+-+-+-+ |
| 1691 | |Q| | | | | | | | |
| 1692 | +-+-+-+-+-+-+-+-+ |
| 1693 | | | | | | |Q| | | |
| 1694 | +-+-+-+-+-+-+-+-+ |
| 1695 | | | | | | | | |Q| |
| 1696 | +-+-+-+-+-+-+-+-+ |
| 1697 | | | |Q| | | | | | |
| 1698 | +-+-+-+-+-+-+-+-+ |
| 1699 | | | | | | | |Q| | |
| 1700 | +-+-+-+-+-+-+-+-+ |
| 1701 | | | | |Q| | | | | |
| 1702 | +-+-+-+-+-+-+-+-+ |
| 1703 | | |Q| | | | | | | |
| 1704 | +-+-+-+-+-+-+-+-+ |
| 1705 | | | | | |Q| | | | |
| 1706 | +-+-+-+-+-+-+-+-+ |
| 1707 | |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1708 | >>> print(count, "solutions in all.") |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1709 | 92 solutions in all. |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1710 | |
| 1711 | And run a Knight's Tour on a 10x10 board. Note that there are about |
| 1712 | 20,000 solutions even on a 6x6 board, so don't dare run this to exhaustion. |
| 1713 | |
Tim Peters | 9a8c8e2 | 2001-07-13 09:12:12 +0000 | [diff] [blame] | 1714 | >>> k = Knights(10, 10) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1715 | >>> LIMIT = 2 |
| 1716 | >>> count = 0 |
| 1717 | >>> for x in k.solve(): |
| 1718 | ... count += 1 |
| 1719 | ... if count <= LIMIT: |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1720 | ... print("Solution", count) |
unknown | 3156956 | 2001-07-04 22:11:22 +0000 | [diff] [blame] | 1721 | ... k.printsolution(x) |
| 1722 | ... else: |
| 1723 | ... break |
| 1724 | Solution 1 |
| 1725 | +---+---+---+---+---+---+---+---+---+---+ |
| 1726 | | 1| 58| 27| 34| 3| 40| 29| 10| 5| 8| |
| 1727 | +---+---+---+---+---+---+---+---+---+---+ |
| 1728 | | 26| 35| 2| 57| 28| 33| 4| 7| 30| 11| |
| 1729 | +---+---+---+---+---+---+---+---+---+---+ |
| 1730 | | 59|100| 73| 36| 41| 56| 39| 32| 9| 6| |
| 1731 | +---+---+---+---+---+---+---+---+---+---+ |
| 1732 | | 74| 25| 60| 55| 72| 37| 42| 49| 12| 31| |
| 1733 | +---+---+---+---+---+---+---+---+---+---+ |
| 1734 | | 61| 86| 99| 76| 63| 52| 47| 38| 43| 50| |
| 1735 | +---+---+---+---+---+---+---+---+---+---+ |
| 1736 | | 24| 75| 62| 85| 54| 71| 64| 51| 48| 13| |
| 1737 | +---+---+---+---+---+---+---+---+---+---+ |
| 1738 | | 87| 98| 91| 80| 77| 84| 53| 46| 65| 44| |
| 1739 | +---+---+---+---+---+---+---+---+---+---+ |
| 1740 | | 90| 23| 88| 95| 70| 79| 68| 83| 14| 17| |
| 1741 | +---+---+---+---+---+---+---+---+---+---+ |
| 1742 | | 97| 92| 21| 78| 81| 94| 19| 16| 45| 66| |
| 1743 | +---+---+---+---+---+---+---+---+---+---+ |
| 1744 | | 22| 89| 96| 93| 20| 69| 82| 67| 18| 15| |
| 1745 | +---+---+---+---+---+---+---+---+---+---+ |
| 1746 | Solution 2 |
| 1747 | +---+---+---+---+---+---+---+---+---+---+ |
| 1748 | | 1| 58| 27| 34| 3| 40| 29| 10| 5| 8| |
| 1749 | +---+---+---+---+---+---+---+---+---+---+ |
| 1750 | | 26| 35| 2| 57| 28| 33| 4| 7| 30| 11| |
| 1751 | +---+---+---+---+---+---+---+---+---+---+ |
| 1752 | | 59|100| 73| 36| 41| 56| 39| 32| 9| 6| |
| 1753 | +---+---+---+---+---+---+---+---+---+---+ |
| 1754 | | 74| 25| 60| 55| 72| 37| 42| 49| 12| 31| |
| 1755 | +---+---+---+---+---+---+---+---+---+---+ |
| 1756 | | 61| 86| 99| 76| 63| 52| 47| 38| 43| 50| |
| 1757 | +---+---+---+---+---+---+---+---+---+---+ |
| 1758 | | 24| 75| 62| 85| 54| 71| 64| 51| 48| 13| |
| 1759 | +---+---+---+---+---+---+---+---+---+---+ |
| 1760 | | 87| 98| 89| 80| 77| 84| 53| 46| 65| 44| |
| 1761 | +---+---+---+---+---+---+---+---+---+---+ |
| 1762 | | 90| 23| 92| 95| 70| 79| 68| 83| 14| 17| |
| 1763 | +---+---+---+---+---+---+---+---+---+---+ |
| 1764 | | 97| 88| 21| 78| 81| 94| 19| 16| 45| 66| |
| 1765 | +---+---+---+---+---+---+---+---+---+---+ |
| 1766 | | 22| 91| 96| 93| 20| 69| 82| 67| 18| 15| |
| 1767 | +---+---+---+---+---+---+---+---+---+---+ |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 1768 | """ |
| 1769 | |
Fred Drake | 56d1266 | 2002-08-09 18:37:10 +0000 | [diff] [blame] | 1770 | weakref_tests = """\ |
| 1771 | Generators are weakly referencable: |
| 1772 | |
| 1773 | >>> import weakref |
| 1774 | >>> def gen(): |
| 1775 | ... yield 'foo!' |
| 1776 | ... |
| 1777 | >>> wr = weakref.ref(gen) |
| 1778 | >>> wr() is gen |
| 1779 | True |
| 1780 | >>> p = weakref.proxy(gen) |
| 1781 | |
| 1782 | Generator-iterators are weakly referencable as well: |
| 1783 | |
| 1784 | >>> gi = gen() |
| 1785 | >>> wr = weakref.ref(gi) |
| 1786 | >>> wr() is gi |
| 1787 | True |
| 1788 | >>> p = weakref.proxy(gi) |
| 1789 | >>> list(p) |
| 1790 | ['foo!'] |
| 1791 | |
| 1792 | """ |
| 1793 | |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1794 | coroutine_tests = """\ |
| 1795 | Sending a value into a started generator: |
| 1796 | |
| 1797 | >>> def f(): |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1798 | ... print((yield 1)) |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1799 | ... yield 2 |
| 1800 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1801 | >>> next(g) |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1802 | 1 |
| 1803 | >>> g.send(42) |
| 1804 | 42 |
| 1805 | 2 |
| 1806 | |
| 1807 | Sending a value into a new generator produces a TypeError: |
| 1808 | |
| 1809 | >>> f().send("foo") |
| 1810 | Traceback (most recent call last): |
| 1811 | ... |
| 1812 | TypeError: can't send non-None value to a just-started generator |
| 1813 | |
| 1814 | |
| 1815 | Yield by itself yields None: |
| 1816 | |
| 1817 | >>> def f(): yield |
| 1818 | >>> list(f()) |
| 1819 | [None] |
| 1820 | |
| 1821 | |
Serhiy Storchaka | 73a7e9b | 2017-12-01 06:54:17 +0200 | [diff] [blame] | 1822 | Yield is allowed only in the outermost iterable in generator expression: |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1823 | |
| 1824 | >>> def f(): list(i for i in [(yield 26)]) |
| 1825 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 1826 | <class 'generator'> |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1827 | |
| 1828 | |
Thomas Wouters | 0e3f591 | 2006-08-11 14:57:12 +0000 | [diff] [blame] | 1829 | A yield expression with augmented assignment. |
| 1830 | |
| 1831 | >>> def coroutine(seq): |
| 1832 | ... count = 0 |
| 1833 | ... while count < 200: |
| 1834 | ... count += yield |
| 1835 | ... seq.append(count) |
| 1836 | >>> seq = [] |
| 1837 | >>> c = coroutine(seq) |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1838 | >>> next(c) |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1839 | >>> print(seq) |
Thomas Wouters | 0e3f591 | 2006-08-11 14:57:12 +0000 | [diff] [blame] | 1840 | [] |
| 1841 | >>> c.send(10) |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1842 | >>> print(seq) |
Thomas Wouters | 0e3f591 | 2006-08-11 14:57:12 +0000 | [diff] [blame] | 1843 | [10] |
| 1844 | >>> c.send(10) |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1845 | >>> print(seq) |
Thomas Wouters | 0e3f591 | 2006-08-11 14:57:12 +0000 | [diff] [blame] | 1846 | [10, 20] |
| 1847 | >>> c.send(10) |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1848 | >>> print(seq) |
Thomas Wouters | 0e3f591 | 2006-08-11 14:57:12 +0000 | [diff] [blame] | 1849 | [10, 20, 30] |
| 1850 | |
| 1851 | |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1852 | Check some syntax errors for yield expressions: |
| 1853 | |
| 1854 | >>> f=lambda: (yield 1),(yield 2) |
| 1855 | Traceback (most recent call last): |
| 1856 | ... |
Guido van Rossum | 33d2689 | 2007-08-05 15:29:28 +0000 | [diff] [blame] | 1857 | SyntaxError: 'yield' outside function |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1858 | |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1859 | >>> def f(): x = yield = y |
| 1860 | Traceback (most recent call last): |
| 1861 | ... |
Guido van Rossum | 33d2689 | 2007-08-05 15:29:28 +0000 | [diff] [blame] | 1862 | SyntaxError: assignment to yield expression not possible |
Thomas Wouters | 0e3f591 | 2006-08-11 14:57:12 +0000 | [diff] [blame] | 1863 | |
| 1864 | >>> def f(): (yield bar) = y |
| 1865 | Traceback (most recent call last): |
| 1866 | ... |
Serhiy Storchaka | 97f1efb | 2018-11-20 19:27:16 +0200 | [diff] [blame] | 1867 | SyntaxError: cannot assign to yield expression |
Thomas Wouters | 0e3f591 | 2006-08-11 14:57:12 +0000 | [diff] [blame] | 1868 | |
| 1869 | >>> def f(): (yield bar) += y |
| 1870 | Traceback (most recent call last): |
| 1871 | ... |
Serhiy Storchaka | 97f1efb | 2018-11-20 19:27:16 +0200 | [diff] [blame] | 1872 | SyntaxError: cannot assign to yield expression |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1873 | |
| 1874 | |
| 1875 | Now check some throw() conditions: |
| 1876 | |
| 1877 | >>> def f(): |
| 1878 | ... while True: |
| 1879 | ... try: |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1880 | ... print((yield)) |
Guido van Rossum | b940e11 | 2007-01-10 16:19:56 +0000 | [diff] [blame] | 1881 | ... except ValueError as v: |
Guido van Rossum | c420b2f | 2007-02-09 22:09:01 +0000 | [diff] [blame] | 1882 | ... print("caught ValueError (%s)" % (v)) |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1883 | >>> import sys |
| 1884 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1885 | >>> next(g) |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1886 | |
| 1887 | >>> g.throw(ValueError) # type only |
| 1888 | caught ValueError () |
| 1889 | |
| 1890 | >>> g.throw(ValueError("xyz")) # value only |
| 1891 | caught ValueError (xyz) |
| 1892 | |
| 1893 | >>> g.throw(ValueError, ValueError(1)) # value+matching type |
| 1894 | caught ValueError (1) |
| 1895 | |
| 1896 | >>> g.throw(ValueError, TypeError(1)) # mismatched type, rewrapped |
| 1897 | caught ValueError (1) |
| 1898 | |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 1899 | >>> g.throw(ValueError, ValueError(1), None) # explicit None traceback |
| 1900 | caught ValueError (1) |
| 1901 | |
Tim Peters | e9fe7e0 | 2005-08-07 03:04:58 +0000 | [diff] [blame] | 1902 | >>> g.throw(ValueError(1), "foo") # bad args |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1903 | Traceback (most recent call last): |
| 1904 | ... |
| 1905 | TypeError: instance exception may not have a separate value |
| 1906 | |
Tim Peters | e9fe7e0 | 2005-08-07 03:04:58 +0000 | [diff] [blame] | 1907 | >>> g.throw(ValueError, "foo", 23) # bad args |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1908 | Traceback (most recent call last): |
| 1909 | ... |
| 1910 | TypeError: throw() third argument must be a traceback object |
| 1911 | |
Guido van Rossum | bf12cdb | 2006-08-17 20:24:18 +0000 | [diff] [blame] | 1912 | >>> g.throw("abc") |
| 1913 | Traceback (most recent call last): |
| 1914 | ... |
| 1915 | TypeError: exceptions must be classes or instances deriving from BaseException, not str |
| 1916 | |
| 1917 | >>> g.throw(0) |
| 1918 | Traceback (most recent call last): |
| 1919 | ... |
| 1920 | TypeError: exceptions must be classes or instances deriving from BaseException, not int |
| 1921 | |
| 1922 | >>> g.throw(list) |
| 1923 | Traceback (most recent call last): |
| 1924 | ... |
| 1925 | TypeError: exceptions must be classes or instances deriving from BaseException, not type |
| 1926 | |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1927 | >>> def throw(g,exc): |
| 1928 | ... try: |
| 1929 | ... raise exc |
| 1930 | ... except: |
| 1931 | ... g.throw(*sys.exc_info()) |
Tim Peters | e9fe7e0 | 2005-08-07 03:04:58 +0000 | [diff] [blame] | 1932 | >>> throw(g,ValueError) # do it with traceback included |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1933 | caught ValueError () |
| 1934 | |
| 1935 | >>> g.send(1) |
| 1936 | 1 |
| 1937 | |
Tim Peters | e9fe7e0 | 2005-08-07 03:04:58 +0000 | [diff] [blame] | 1938 | >>> throw(g,TypeError) # terminate the generator |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1939 | Traceback (most recent call last): |
| 1940 | ... |
| 1941 | TypeError |
| 1942 | |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1943 | >>> print(g.gi_frame) |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1944 | None |
| 1945 | |
| 1946 | >>> g.send(2) |
| 1947 | Traceback (most recent call last): |
| 1948 | ... |
| 1949 | StopIteration |
| 1950 | |
Tim Peters | e9fe7e0 | 2005-08-07 03:04:58 +0000 | [diff] [blame] | 1951 | >>> g.throw(ValueError,6) # throw on closed generator |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1952 | Traceback (most recent call last): |
| 1953 | ... |
| 1954 | ValueError: 6 |
| 1955 | |
Tim Peters | e9fe7e0 | 2005-08-07 03:04:58 +0000 | [diff] [blame] | 1956 | >>> f().throw(ValueError,7) # throw on just-opened generator |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1957 | Traceback (most recent call last): |
| 1958 | ... |
| 1959 | ValueError: 7 |
| 1960 | |
Antoine Pitrou | 551ba20 | 2011-10-18 16:40:50 +0200 | [diff] [blame] | 1961 | Plain "raise" inside a generator should preserve the traceback (#13188). |
| 1962 | The traceback should have 3 levels: |
| 1963 | - g.throw() |
| 1964 | - f() |
| 1965 | - 1/0 |
| 1966 | |
| 1967 | >>> def f(): |
| 1968 | ... try: |
| 1969 | ... yield |
| 1970 | ... except: |
| 1971 | ... raise |
| 1972 | >>> g = f() |
| 1973 | >>> try: |
| 1974 | ... 1/0 |
| 1975 | ... except ZeroDivisionError as v: |
| 1976 | ... try: |
| 1977 | ... g.throw(v) |
| 1978 | ... except Exception as w: |
| 1979 | ... tb = w.__traceback__ |
| 1980 | >>> levels = 0 |
| 1981 | >>> while tb: |
| 1982 | ... levels += 1 |
| 1983 | ... tb = tb.tb_next |
| 1984 | >>> levels |
| 1985 | 3 |
| 1986 | |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1987 | Now let's try closing a generator: |
| 1988 | |
| 1989 | >>> def f(): |
| 1990 | ... try: yield |
| 1991 | ... except GeneratorExit: |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 1992 | ... print("exiting") |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1993 | |
| 1994 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 1995 | >>> next(g) |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 1996 | >>> g.close() |
| 1997 | exiting |
| 1998 | >>> g.close() # should be no-op now |
| 1999 | |
| 2000 | >>> f().close() # close on just-opened generator should be fine |
| 2001 | |
Tim Peters | e9fe7e0 | 2005-08-07 03:04:58 +0000 | [diff] [blame] | 2002 | >>> def f(): yield # an even simpler generator |
| 2003 | >>> f().close() # close before opening |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2004 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 2005 | >>> next(g) |
Tim Peters | e9fe7e0 | 2005-08-07 03:04:58 +0000 | [diff] [blame] | 2006 | >>> g.close() # close normally |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2007 | |
| 2008 | And finalization: |
| 2009 | |
| 2010 | >>> def f(): |
| 2011 | ... try: yield |
| 2012 | ... finally: |
Guido van Rossum | 7131f84 | 2007-02-09 20:13:25 +0000 | [diff] [blame] | 2013 | ... print("exiting") |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2014 | |
| 2015 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 2016 | >>> next(g) |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2017 | >>> del g |
| 2018 | exiting |
| 2019 | |
| 2020 | |
Christian Heimes | cbf3b5c | 2007-12-03 21:02:03 +0000 | [diff] [blame] | 2021 | GeneratorExit is not caught by except Exception: |
| 2022 | |
| 2023 | >>> def f(): |
| 2024 | ... try: yield |
| 2025 | ... except Exception: |
| 2026 | ... print('except') |
| 2027 | ... finally: |
| 2028 | ... print('finally') |
| 2029 | |
| 2030 | >>> g = f() |
| 2031 | >>> next(g) |
| 2032 | >>> del g |
| 2033 | finally |
| 2034 | |
| 2035 | |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2036 | Now let's try some ill-behaved generators: |
| 2037 | |
| 2038 | >>> def f(): |
| 2039 | ... try: yield |
| 2040 | ... except GeneratorExit: |
| 2041 | ... yield "foo!" |
| 2042 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 2043 | >>> next(g) |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2044 | >>> g.close() |
| 2045 | Traceback (most recent call last): |
| 2046 | ... |
| 2047 | RuntimeError: generator ignored GeneratorExit |
| 2048 | >>> g.close() |
| 2049 | |
| 2050 | |
| 2051 | Our ill-behaved code should be invoked during GC: |
| 2052 | |
Victor Stinner | 0025350 | 2019-06-03 03:51:43 +0200 | [diff] [blame] | 2053 | >>> with support.catch_unraisable_exception() as cm: |
| 2054 | ... g = f() |
| 2055 | ... next(g) |
| 2056 | ... del g |
| 2057 | ... |
| 2058 | ... cm.unraisable.exc_type == RuntimeError |
| 2059 | ... "generator ignored GeneratorExit" in str(cm.unraisable.exc_value) |
| 2060 | ... cm.unraisable.exc_traceback is not None |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2061 | True |
Victor Stinner | 0025350 | 2019-06-03 03:51:43 +0200 | [diff] [blame] | 2062 | True |
| 2063 | True |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2064 | |
| 2065 | And errors thrown during closing should propagate: |
| 2066 | |
| 2067 | >>> def f(): |
| 2068 | ... try: yield |
| 2069 | ... except GeneratorExit: |
| 2070 | ... raise TypeError("fie!") |
| 2071 | >>> g = f() |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 2072 | >>> next(g) |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2073 | >>> g.close() |
| 2074 | Traceback (most recent call last): |
| 2075 | ... |
| 2076 | TypeError: fie! |
| 2077 | |
| 2078 | |
| 2079 | Ensure that various yield expression constructs make their |
| 2080 | enclosing function a generator: |
| 2081 | |
| 2082 | >>> def f(): x += yield |
| 2083 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 2084 | <class 'generator'> |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2085 | |
| 2086 | >>> def f(): x = yield |
| 2087 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 2088 | <class 'generator'> |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2089 | |
| 2090 | >>> def f(): lambda x=(yield): 1 |
| 2091 | >>> type(f()) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 2092 | <class 'generator'> |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2093 | |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2094 | >>> def f(d): d[(yield "a")] = d[(yield "b")] = 27 |
| 2095 | >>> data = [1,2] |
| 2096 | >>> g = f(data) |
| 2097 | >>> type(g) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 2098 | <class 'generator'> |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2099 | >>> g.send(None) |
| 2100 | 'a' |
| 2101 | >>> data |
| 2102 | [1, 2] |
| 2103 | >>> g.send(0) |
| 2104 | 'b' |
| 2105 | >>> data |
| 2106 | [27, 2] |
| 2107 | >>> try: g.send(1) |
| 2108 | ... except StopIteration: pass |
| 2109 | >>> data |
| 2110 | [27, 27] |
| 2111 | |
| 2112 | """ |
| 2113 | |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 2114 | refleaks_tests = """ |
| 2115 | Prior to adding cycle-GC support to itertools.tee, this code would leak |
| 2116 | references. We add it to the standard suite so the routine refleak-tests |
| 2117 | would trigger if it starts being uncleanable again. |
| 2118 | |
| 2119 | >>> import itertools |
| 2120 | >>> def leak(): |
| 2121 | ... class gen: |
| 2122 | ... def __iter__(self): |
| 2123 | ... return self |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 2124 | ... def __next__(self): |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 2125 | ... return self.item |
| 2126 | ... g = gen() |
| 2127 | ... head, tail = itertools.tee(g) |
| 2128 | ... g.item = head |
| 2129 | ... return head |
| 2130 | >>> it = leak() |
| 2131 | |
| 2132 | Make sure to also test the involvement of the tee-internal teedataobject, |
| 2133 | which stores returned items. |
| 2134 | |
Georg Brandl | a18af4e | 2007-04-21 15:47:16 +0000 | [diff] [blame] | 2135 | >>> item = next(it) |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 2136 | |
| 2137 | |
| 2138 | |
| 2139 | This test leaked at one point due to generator finalization/destruction. |
| 2140 | It was copied from Lib/test/leakers/test_generator_cycle.py before the file |
| 2141 | was removed. |
| 2142 | |
| 2143 | >>> def leak(): |
| 2144 | ... def gen(): |
| 2145 | ... while True: |
| 2146 | ... yield g |
| 2147 | ... g = gen() |
| 2148 | |
| 2149 | >>> leak() |
| 2150 | |
| 2151 | |
| 2152 | |
| 2153 | This test isn't really generator related, but rather exception-in-cleanup |
| 2154 | related. The coroutine tests (above) just happen to cause an exception in |
| 2155 | the generator's __del__ (tp_del) method. We can also test for this |
| 2156 | explicitly, without generators. We do have to redirect stderr to avoid |
| 2157 | printing warnings and to doublecheck that we actually tested what we wanted |
| 2158 | to test. |
| 2159 | |
Victor Stinner | e4d300e | 2019-05-22 23:44:02 +0200 | [diff] [blame] | 2160 | >>> from test import support |
| 2161 | >>> class Leaker: |
| 2162 | ... def __del__(self): |
| 2163 | ... def invoke(message): |
| 2164 | ... raise RuntimeError(message) |
| 2165 | ... invoke("del failed") |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 2166 | ... |
Victor Stinner | e4d300e | 2019-05-22 23:44:02 +0200 | [diff] [blame] | 2167 | >>> with support.catch_unraisable_exception() as cm: |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 2168 | ... l = Leaker() |
| 2169 | ... del l |
Victor Stinner | e4d300e | 2019-05-22 23:44:02 +0200 | [diff] [blame] | 2170 | ... |
| 2171 | ... cm.unraisable.object == Leaker.__del__ |
| 2172 | ... cm.unraisable.exc_type == RuntimeError |
| 2173 | ... str(cm.unraisable.exc_value) == "del failed" |
| 2174 | ... cm.unraisable.exc_traceback is not None |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 2175 | True |
| 2176 | True |
Andrew Svetlov | 76bcff2 | 2012-11-03 15:56:05 +0200 | [diff] [blame] | 2177 | True |
| 2178 | True |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 2179 | |
| 2180 | |
| 2181 | These refleak tests should perhaps be in a testfile of their own, |
| 2182 | test_generators just happened to be the test that drew these out. |
| 2183 | |
| 2184 | """ |
| 2185 | |
Tim Peters | f6ed074 | 2001-06-27 07:17:57 +0000 | [diff] [blame] | 2186 | __test__ = {"tut": tutorial_tests, |
| 2187 | "pep": pep_tests, |
| 2188 | "email": email_tests, |
| 2189 | "fun": fun_tests, |
Tim Peters | be4f0a7 | 2001-06-29 02:41:16 +0000 | [diff] [blame] | 2190 | "syntax": syntax_tests, |
Fred Drake | 56d1266 | 2002-08-09 18:37:10 +0000 | [diff] [blame] | 2191 | "conjoin": conjoin_tests, |
| 2192 | "weakref": weakref_tests, |
Phillip J. Eby | 0d6615f | 2005-08-02 00:46:46 +0000 | [diff] [blame] | 2193 | "coroutine": coroutine_tests, |
Thomas Wouters | 49fd7fa | 2006-04-21 10:40:58 +0000 | [diff] [blame] | 2194 | "refleaks": refleaks_tests, |
Fred Drake | 56d1266 | 2002-08-09 18:37:10 +0000 | [diff] [blame] | 2195 | } |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 2196 | |
| 2197 | # Magic test name that regrtest.py invokes *after* importing this module. |
| 2198 | # This worms around a bootstrap problem. |
| 2199 | # Note that doctest and regrtest both look in sys.argv for a "-v" argument, |
| 2200 | # so this works as expected in both ways of running regrtest. |
Tim Peters | a0a6222 | 2001-09-09 06:12:01 +0000 | [diff] [blame] | 2201 | def test_main(verbose=None): |
Benjamin Peterson | ee8712c | 2008-05-20 21:35:26 +0000 | [diff] [blame] | 2202 | from test import support, test_generators |
Antoine Pitrou | 796564c | 2013-07-30 19:59:21 +0200 | [diff] [blame] | 2203 | support.run_unittest(__name__) |
Benjamin Peterson | ab078e9 | 2016-07-13 21:13:29 -0700 | [diff] [blame] | 2204 | support.run_doctest(test_generators, verbose) |
Tim Peters | 1def351 | 2001-06-23 20:27:04 +0000 | [diff] [blame] | 2205 | |
| 2206 | # This part isn't needed for regrtest, but for running the test directly. |
| 2207 | if __name__ == "__main__": |
Tim Peters | a0a6222 | 2001-09-09 06:12:01 +0000 | [diff] [blame] | 2208 | test_main(1) |