Guido van Rossum | 52cc1d8 | 2007-03-18 15:41:51 +0000 | [diff] [blame] | 1 | doctests = """ |
| 2 | |
| 3 | Basic class construction. |
| 4 | |
| 5 | >>> class C: |
| 6 | ... def meth(self): print("Hello") |
| 7 | ... |
| 8 | >>> C.__class__ is type |
| 9 | True |
| 10 | >>> a = C() |
| 11 | >>> a.__class__ is C |
| 12 | True |
| 13 | >>> a.meth() |
| 14 | Hello |
| 15 | >>> |
| 16 | |
| 17 | Use *args notation for the bases. |
| 18 | |
| 19 | >>> class A: pass |
| 20 | >>> class B: pass |
| 21 | >>> bases = (A, B) |
| 22 | >>> class C(*bases): pass |
| 23 | >>> C.__bases__ == bases |
| 24 | True |
| 25 | >>> |
| 26 | |
| 27 | Use a trivial metaclass. |
| 28 | |
| 29 | >>> class M(type): |
| 30 | ... pass |
| 31 | ... |
| 32 | >>> class C(metaclass=M): |
| 33 | ... def meth(self): print("Hello") |
| 34 | ... |
| 35 | >>> C.__class__ is M |
| 36 | True |
| 37 | >>> a = C() |
| 38 | >>> a.__class__ is C |
| 39 | True |
| 40 | >>> a.meth() |
| 41 | Hello |
| 42 | >>> |
| 43 | |
| 44 | Use **kwds notation for the metaclass keyword. |
| 45 | |
| 46 | >>> kwds = {'metaclass': M} |
| 47 | >>> class C(**kwds): pass |
| 48 | ... |
| 49 | >>> C.__class__ is M |
| 50 | True |
| 51 | >>> a = C() |
| 52 | >>> a.__class__ is C |
| 53 | True |
| 54 | >>> |
| 55 | |
| 56 | Use a metaclass with a __prepare__ static method. |
| 57 | |
| 58 | >>> class M(type): |
| 59 | ... @staticmethod |
| 60 | ... def __prepare__(*args, **kwds): |
| 61 | ... print("Prepare called:", args, kwds) |
| 62 | ... return dict() |
| 63 | ... def __new__(cls, name, bases, namespace, **kwds): |
| 64 | ... print("New called:", kwds) |
| 65 | ... return type.__new__(cls, name, bases, namespace) |
Guido van Rossum | d8faa36 | 2007-04-27 19:54:29 +0000 | [diff] [blame] | 66 | ... def __init__(cls, *args, **kwds): |
| 67 | ... pass |
Guido van Rossum | 52cc1d8 | 2007-03-18 15:41:51 +0000 | [diff] [blame] | 68 | ... |
| 69 | >>> class C(metaclass=M): |
| 70 | ... def meth(self): print("Hello") |
| 71 | ... |
| 72 | Prepare called: ('C', ()) {} |
| 73 | New called: {} |
| 74 | >>> |
| 75 | |
| 76 | Also pass another keyword. |
| 77 | |
| 78 | >>> class C(object, metaclass=M, other="haha"): |
| 79 | ... pass |
| 80 | ... |
Martin v. Löwis | 250ad61 | 2008-04-07 05:43:42 +0000 | [diff] [blame] | 81 | Prepare called: ('C', (<class 'object'>,)) {'other': 'haha'} |
Guido van Rossum | 52cc1d8 | 2007-03-18 15:41:51 +0000 | [diff] [blame] | 82 | New called: {'other': 'haha'} |
| 83 | >>> C.__class__ is M |
| 84 | True |
| 85 | >>> C.__bases__ == (object,) |
| 86 | True |
| 87 | >>> a = C() |
| 88 | >>> a.__class__ is C |
| 89 | True |
| 90 | >>> |
| 91 | |
| 92 | Check that build_class doesn't mutate the kwds dict. |
| 93 | |
| 94 | >>> kwds = {'metaclass': type} |
| 95 | >>> class C(**kwds): pass |
| 96 | ... |
| 97 | >>> kwds == {'metaclass': type} |
| 98 | True |
| 99 | >>> |
| 100 | |
| 101 | Use various combinations of explicit keywords and **kwds. |
| 102 | |
| 103 | >>> bases = (object,) |
| 104 | >>> kwds = {'metaclass': M, 'other': 'haha'} |
| 105 | >>> class C(*bases, **kwds): pass |
| 106 | ... |
Martin v. Löwis | 250ad61 | 2008-04-07 05:43:42 +0000 | [diff] [blame] | 107 | Prepare called: ('C', (<class 'object'>,)) {'other': 'haha'} |
Guido van Rossum | 52cc1d8 | 2007-03-18 15:41:51 +0000 | [diff] [blame] | 108 | New called: {'other': 'haha'} |
| 109 | >>> C.__class__ is M |
| 110 | True |
| 111 | >>> C.__bases__ == (object,) |
| 112 | True |
| 113 | >>> class B: pass |
| 114 | >>> kwds = {'other': 'haha'} |
| 115 | >>> class C(B, metaclass=M, *bases, **kwds): pass |
| 116 | ... |
Martin v. Löwis | 250ad61 | 2008-04-07 05:43:42 +0000 | [diff] [blame] | 117 | Prepare called: ('C', (<class 'test.test_metaclass.B'>, <class 'object'>)) {'other': 'haha'} |
Guido van Rossum | 52cc1d8 | 2007-03-18 15:41:51 +0000 | [diff] [blame] | 118 | New called: {'other': 'haha'} |
| 119 | >>> C.__class__ is M |
| 120 | True |
| 121 | >>> C.__bases__ == (B, object) |
| 122 | True |
| 123 | >>> |
| 124 | |
| 125 | Check for duplicate keywords. |
| 126 | |
| 127 | >>> class C(metaclass=type, metaclass=type): pass |
| 128 | ... |
| 129 | Traceback (most recent call last): |
| 130 | [...] |
Benjamin Peterson | 13b6d0d | 2008-07-01 20:26:36 +0000 | [diff] [blame] | 131 | SyntaxError: keyword argument repeated |
Guido van Rossum | 52cc1d8 | 2007-03-18 15:41:51 +0000 | [diff] [blame] | 132 | >>> |
| 133 | |
| 134 | Another way. |
| 135 | |
| 136 | >>> kwds = {'metaclass': type} |
| 137 | >>> class C(metaclass=type, **kwds): pass |
| 138 | ... |
| 139 | Traceback (most recent call last): |
| 140 | [...] |
| 141 | TypeError: __build_class__() got multiple values for keyword argument 'metaclass' |
| 142 | >>> |
| 143 | |
| 144 | Use a __prepare__ method that returns an instrumented dict. |
| 145 | |
| 146 | >>> class LoggingDict(dict): |
| 147 | ... def __setitem__(self, key, value): |
| 148 | ... print("d[%r] = %r" % (key, value)) |
| 149 | ... dict.__setitem__(self, key, value) |
| 150 | ... |
| 151 | >>> class Meta(type): |
| 152 | ... @staticmethod |
| 153 | ... def __prepare__(name, bases): |
| 154 | ... return LoggingDict() |
| 155 | ... |
| 156 | >>> class C(metaclass=Meta): |
| 157 | ... foo = 2+2 |
| 158 | ... foo = 42 |
| 159 | ... bar = 123 |
| 160 | ... |
| 161 | d['__module__'] = 'test.test_metaclass' |
| 162 | d['foo'] = 4 |
| 163 | d['foo'] = 42 |
| 164 | d['bar'] = 123 |
| 165 | >>> |
| 166 | |
| 167 | Use a metaclass that doesn't derive from type. |
| 168 | |
| 169 | >>> def meta(name, bases, namespace, **kwds): |
| 170 | ... print("meta:", name, bases) |
| 171 | ... print("ns:", sorted(namespace.items())) |
| 172 | ... print("kw:", sorted(kwds.items())) |
| 173 | ... return namespace |
| 174 | ... |
| 175 | >>> class C(metaclass=meta): |
| 176 | ... a = 42 |
| 177 | ... b = 24 |
| 178 | ... |
| 179 | meta: C () |
| 180 | ns: [('__module__', 'test.test_metaclass'), ('a', 42), ('b', 24)] |
| 181 | kw: [] |
| 182 | >>> type(C) is dict |
| 183 | True |
| 184 | >>> print(sorted(C.items())) |
| 185 | [('__module__', 'test.test_metaclass'), ('a', 42), ('b', 24)] |
| 186 | >>> |
| 187 | |
| 188 | And again, with a __prepare__ attribute. |
| 189 | |
| 190 | >>> def prepare(name, bases, **kwds): |
| 191 | ... print("prepare:", name, bases, sorted(kwds.items())) |
| 192 | ... return LoggingDict() |
| 193 | ... |
| 194 | >>> meta.__prepare__ = prepare |
| 195 | >>> class C(metaclass=meta, other="booh"): |
| 196 | ... a = 1 |
| 197 | ... a = 2 |
| 198 | ... b = 3 |
| 199 | ... |
| 200 | prepare: C () [('other', 'booh')] |
| 201 | d['__module__'] = 'test.test_metaclass' |
| 202 | d['a'] = 1 |
| 203 | d['a'] = 2 |
| 204 | d['b'] = 3 |
| 205 | meta: C () |
| 206 | ns: [('__module__', 'test.test_metaclass'), ('a', 2), ('b', 3)] |
| 207 | kw: [('other', 'booh')] |
| 208 | >>> |
| 209 | |
Guido van Rossum | 4737482 | 2007-08-02 16:48:17 +0000 | [diff] [blame] | 210 | The default metaclass must define a __prepare__() method. |
| 211 | |
| 212 | >>> type.__prepare__() |
| 213 | {} |
| 214 | >>> |
| 215 | |
| 216 | Make sure it works with subclassing. |
| 217 | |
| 218 | >>> class M(type): |
| 219 | ... @classmethod |
| 220 | ... def __prepare__(cls, *args, **kwds): |
| 221 | ... d = super().__prepare__(*args, **kwds) |
| 222 | ... d["hello"] = 42 |
| 223 | ... return d |
| 224 | ... |
| 225 | >>> class C(metaclass=M): |
| 226 | ... print(hello) |
| 227 | ... |
| 228 | 42 |
| 229 | >>> print(C.hello) |
| 230 | 42 |
| 231 | >>> |
| 232 | |
Guido van Rossum | 52cc1d8 | 2007-03-18 15:41:51 +0000 | [diff] [blame] | 233 | """ |
| 234 | |
| 235 | __test__ = {'doctests' : doctests} |
| 236 | |
| 237 | def test_main(verbose=False): |
Benjamin Peterson | ee8712c | 2008-05-20 21:35:26 +0000 | [diff] [blame] | 238 | from test import support |
Guido van Rossum | 52cc1d8 | 2007-03-18 15:41:51 +0000 | [diff] [blame] | 239 | from test import test_metaclass |
Benjamin Peterson | ee8712c | 2008-05-20 21:35:26 +0000 | [diff] [blame] | 240 | support.run_doctest(test_metaclass, verbose) |
Guido van Rossum | 52cc1d8 | 2007-03-18 15:41:51 +0000 | [diff] [blame] | 241 | |
| 242 | if __name__ == "__main__": |
| 243 | test_main(verbose=True) |