Lib/test/test_functools.py

import abc
import builtins
import collections
import collections.abc
import copy
from itertools import permutations
import pickle
from random import choice
import sys
from test import support
import threading
import time
import typing
import unittest
import unittest.mock
from weakref import proxy
import contextlib

import functools

py_functools = support.import_fresh_module('functools', blocked=['_functools'])
c_functools = support.import_fresh_module('functools', fresh=['_functools'])

decimal = support.import_fresh_module('decimal', fresh=['_decimal'])

@contextlib.contextmanager
def replaced_module(name, replacement):
    original_module = sys.modules[name]
    sys.modules[name] = replacement
    try:
        yield
    finally:
        sys.modules[name] = original_module

def capture(*args, **kw):
    """capture all positional and keyword arguments"""
    return args, kw


def signature(part):
    """ return the signature of a partial object """
    return (part.func, part.args, part.keywords, part.__dict__)

class MyTuple(tuple):
    pass

class BadTuple(tuple):
    def __add__(self, other):
        return list(self) + list(other)

class MyDict(dict):
    pass


class TestPartial:

    def test_basic_examples(self):
        p = self.partial(capture, 1, 2, a=10, b=20)
        self.assertTrue(callable(p))
        self.assertEqual(p(3, 4, b=30, c=40),
                         ((1, 2, 3, 4), dict(a=10, b=30, c=40)))
        p = self.partial(map, lambda x: x*10)
        self.assertEqual(list(p([1,2,3,4])), [10, 20, 30, 40])

    def test_attributes(self):
        p = self.partial(capture, 1, 2, a=10, b=20)
        # attributes should be readable
        self.assertEqual(p.func, capture)
        self.assertEqual(p.args, (1, 2))
        self.assertEqual(p.keywords, dict(a=10, b=20))

    def test_argument_checking(self):
        self.assertRaises(TypeError, self.partial)     # need at least a func arg
        try:
            self.partial(2)()
        except TypeError:
            pass
        else:
            self.fail('First arg not checked for callability')

    def test_protection_of_callers_dict_argument(self):
        # a caller's dictionary should not be altered by partial
        def func(a=10, b=20):
            return a
        d = {'a':3}
        p = self.partial(func, a=5)
        self.assertEqual(p(**d), 3)
        self.assertEqual(d, {'a':3})
        p(b=7)
        self.assertEqual(d, {'a':3})

    def test_kwargs_copy(self):
        # Issue #29532: Altering a kwarg dictionary passed to a constructor
        # should not affect a partial object after creation
        d = {'a': 3}
        p = self.partial(capture, **d)
        self.assertEqual(p(), ((), {'a': 3}))
        d['a'] = 5
        self.assertEqual(p(), ((), {'a': 3}))

    def test_arg_combinations(self):
        # exercise special code paths for zero args in either partial
        # object or the caller
        p = self.partial(capture)
        self.assertEqual(p(), ((), {}))
        self.assertEqual(p(1,2), ((1,2), {}))
        p = self.partial(capture, 1, 2)
        self.assertEqual(p(), ((1,2), {}))
        self.assertEqual(p(3,4), ((1,2,3,4), {}))

    def test_kw_combinations(self):
        # exercise special code paths for no keyword args in
        # either the partial object or the caller
        p = self.partial(capture)
        self.assertEqual(p.keywords, {})
        self.assertEqual(p(), ((), {}))
        self.assertEqual(p(a=1), ((), {'a':1}))
        p = self.partial(capture, a=1)
        self.assertEqual(p.keywords, {'a':1})
        self.assertEqual(p(), ((), {'a':1}))
        self.assertEqual(p(b=2), ((), {'a':1, 'b':2}))
        # keyword args in the call override those in the partial object
        self.assertEqual(p(a=3, b=2), ((), {'a':3, 'b':2}))

    def test_positional(self):
        # make sure positional arguments are captured correctly
        for args in [(), (0,), (0,1), (0,1,2), (0,1,2,3)]:
            p = self.partial(capture, *args)
            expected = args + ('x',)
            got, empty = p('x')
            self.assertTrue(expected == got and empty == {})

    def test_keyword(self):
        # make sure keyword arguments are captured correctly
        for a in ['a', 0, None, 3.5]:
            p = self.partial(capture, a=a)
            expected = {'a':a,'x':None}
            empty, got = p(x=None)
            self.assertTrue(expected == got and empty == ())

    def test_no_side_effects(self):
        # make sure there are no side effects that affect subsequent calls
        p = self.partial(capture, 0, a=1)
        args1, kw1 = p(1, b=2)
        self.assertTrue(args1 == (0,1) and kw1 == {'a':1,'b':2})
        args2, kw2 = p()
        self.assertTrue(args2 == (0,) and kw2 == {'a':1})

    def test_error_propagation(self):
        def f(x, y):
            x / y
        self.assertRaises(ZeroDivisionError, self.partial(f, 1, 0))
        self.assertRaises(ZeroDivisionError, self.partial(f, 1), 0)
        self.assertRaises(ZeroDivisionError, self.partial(f), 1, 0)
        self.assertRaises(ZeroDivisionError, self.partial(f, y=0), 1)

    def test_weakref(self):
        f = self.partial(int, base=16)
        p = proxy(f)
        self.assertEqual(f.func, p.func)
        f = None
        self.assertRaises(ReferenceError, getattr, p, 'func')

    def test_with_bound_and_unbound_methods(self):
        data = list(map(str, range(10)))
        join = self.partial(str.join, '')
        self.assertEqual(join(data), '0123456789')
        join = self.partial(''.join)
        self.assertEqual(join(data), '0123456789')

    def test_nested_optimization(self):
        partial = self.partial
        inner = partial(signature, 'asdf')
        nested = partial(inner, bar=True)
        flat = partial(signature, 'asdf', bar=True)
        self.assertEqual(signature(nested), signature(flat))

    def test_nested_partial_with_attribute(self):
        # see issue 25137
        partial = self.partial

        def foo(bar):
            return bar

        p = partial(foo, 'first')
        p2 = partial(p, 'second')
        p2.new_attr = 'spam'
        self.assertEqual(p2.new_attr, 'spam')

    def test_repr(self):
        args = (object(), object())
        args_repr = ', '.join(repr(a) for a in args)
        kwargs = {'a': object(), 'b': object()}
        kwargs_reprs = ['a={a!r}, b={b!r}'.format_map(kwargs),
                        'b={b!r}, a={a!r}'.format_map(kwargs)]
        if self.partial in (c_functools.partial, py_functools.partial):
            name = 'functools.partial'
        else:
            name = self.partial.__name__

        f = self.partial(capture)
        self.assertEqual(f'{name}({capture!r})', repr(f))

        f = self.partial(capture, *args)
        self.assertEqual(f'{name}({capture!r}, {args_repr})', repr(f))

        f = self.partial(capture, **kwargs)
        self.assertIn(repr(f),
                      [f'{name}({capture!r}, {kwargs_repr})'
                       for kwargs_repr in kwargs_reprs])

        f = self.partial(capture, *args, **kwargs)
        self.assertIn(repr(f),
                      [f'{name}({capture!r}, {args_repr}, {kwargs_repr})'
                       for kwargs_repr in kwargs_reprs])

    def test_recursive_repr(self):
        if self.partial in (c_functools.partial, py_functools.partial):
            name = 'functools.partial'
        else:
            name = self.partial.__name__

        f = self.partial(capture)
        f.__setstate__((f, (), {}, {}))
        try:
            self.assertEqual(repr(f), '%s(...)' % (name,))
        finally:
            f.__setstate__((capture, (), {}, {}))

        f = self.partial(capture)
        f.__setstate__((capture, (f,), {}, {}))
        try:
            self.assertEqual(repr(f), '%s(%r, ...)' % (name, capture,))
        finally:
            f.__setstate__((capture, (), {}, {}))

        f = self.partial(capture)
        f.__setstate__((capture, (), {'a': f}, {}))
        try:
            self.assertEqual(repr(f), '%s(%r, a=...)' % (name, capture,))
        finally:
            f.__setstate__((capture, (), {}, {}))

    def test_pickle(self):
        with self.AllowPickle():
            f = self.partial(signature, ['asdf'], bar=[True])
            f.attr = []
            for proto in range(pickle.HIGHEST_PROTOCOL + 1):
                f_copy = pickle.loads(pickle.dumps(f, proto))
                self.assertEqual(signature(f_copy), signature(f))

    def test_copy(self):
        f = self.partial(signature, ['asdf'], bar=[True])
        f.attr = []
        f_copy = copy.copy(f)
        self.assertEqual(signature(f_copy), signature(f))
        self.assertIs(f_copy.attr, f.attr)
        self.assertIs(f_copy.args, f.args)
        self.assertIs(f_copy.keywords, f.keywords)

    def test_deepcopy(self):
        f = self.partial(signature, ['asdf'], bar=[True])
        f.attr = []
        f_copy = copy.deepcopy(f)
        self.assertEqual(signature(f_copy), signature(f))
        self.assertIsNot(f_copy.attr, f.attr)
        self.assertIsNot(f_copy.args, f.args)
        self.assertIsNot(f_copy.args[0], f.args[0])
        self.assertIsNot(f_copy.keywords, f.keywords)
        self.assertIsNot(f_copy.keywords['bar'], f.keywords['bar'])

    def test_setstate(self):
        f = self.partial(signature)
        f.__setstate__((capture, (1,), dict(a=10), dict(attr=[])))

        self.assertEqual(signature(f),
                         (capture, (1,), dict(a=10), dict(attr=[])))
        self.assertEqual(f(2, b=20), ((1, 2), {'a': 10, 'b': 20}))

        f.__setstate__((capture, (1,), dict(a=10), None))

        self.assertEqual(signature(f), (capture, (1,), dict(a=10), {}))
        self.assertEqual(f(2, b=20), ((1, 2), {'a': 10, 'b': 20}))

        f.__setstate__((capture, (1,), None, None))
        #self.assertEqual(signature(f), (capture, (1,), {}, {}))
        self.assertEqual(f(2, b=20), ((1, 2), {'b': 20}))
        self.assertEqual(f(2), ((1, 2), {}))
        self.assertEqual(f(), ((1,), {}))

        f.__setstate__((capture, (), {}, None))
        self.assertEqual(signature(f), (capture, (), {}, {}))
        self.assertEqual(f(2, b=20), ((2,), {'b': 20}))
        self.assertEqual(f(2), ((2,), {}))
        self.assertEqual(f(), ((), {}))

    def test_setstate_errors(self):
        f = self.partial(signature)
        self.assertRaises(TypeError, f.__setstate__, (capture, (), {}))
        self.assertRaises(TypeError, f.__setstate__, (capture, (), {}, {}, None))
        self.assertRaises(TypeError, f.__setstate__, [capture, (), {}, None])
        self.assertRaises(TypeError, f.__setstate__, (None, (), {}, None))
        self.assertRaises(TypeError, f.__setstate__, (capture, None, {}, None))
        self.assertRaises(TypeError, f.__setstate__, (capture, [], {}, None))
        self.assertRaises(TypeError, f.__setstate__, (capture, (), [], None))

    def test_setstate_subclasses(self):
        f = self.partial(signature)
        f.__setstate__((capture, MyTuple((1,)), MyDict(a=10), None))
        s = signature(f)
        self.assertEqual(s, (capture, (1,), dict(a=10), {}))
        self.assertIs(type(s[1]), tuple)
        self.assertIs(type(s[2]), dict)
        r = f()
        self.assertEqual(r, ((1,), {'a': 10}))
        self.assertIs(type(r[0]), tuple)
        self.assertIs(type(r[1]), dict)

        f.__setstate__((capture, BadTuple((1,)), {}, None))
        s = signature(f)
        self.assertEqual(s, (capture, (1,), {}, {}))
        self.assertIs(type(s[1]), tuple)
        r = f(2)
        self.assertEqual(r, ((1, 2), {}))
        self.assertIs(type(r[0]), tuple)

    def test_recursive_pickle(self):
        with self.AllowPickle():
            f = self.partial(capture)
            f.__setstate__((f, (), {}, {}))
            try:
                for proto in range(pickle.HIGHEST_PROTOCOL + 1):
                    with self.assertRaises(RecursionError):
                        pickle.dumps(f, proto)
            finally:
                f.__setstate__((capture, (), {}, {}))

            f = self.partial(capture)
            f.__setstate__((capture, (f,), {}, {}))
            try:
                for proto in range(pickle.HIGHEST_PROTOCOL + 1):
                    f_copy = pickle.loads(pickle.dumps(f, proto))
                    try:
                        self.assertIs(f_copy.args[0], f_copy)
                    finally:
                        f_copy.__setstate__((capture, (), {}, {}))
            finally:
                f.__setstate__((capture, (), {}, {}))

            f = self.partial(capture)
            f.__setstate__((capture, (), {'a': f}, {}))
            try:
                for proto in range(pickle.HIGHEST_PROTOCOL + 1):
                    f_copy = pickle.loads(pickle.dumps(f, proto))
                    try:
                        self.assertIs(f_copy.keywords['a'], f_copy)
                    finally:
                        f_copy.__setstate__((capture, (), {}, {}))
            finally:
                f.__setstate__((capture, (), {}, {}))

    # Issue 6083: Reference counting bug
    def test_setstate_refcount(self):
        class BadSequence:
            def __len__(self):
                return 4
            def __getitem__(self, key):
                if key == 0:
                    return max
                elif key == 1:
                    return tuple(range(1000000))
                elif key in (2, 3):
                    return {}
                raise IndexError

        f = self.partial(object)
        self.assertRaises(TypeError, f.__setstate__, BadSequence())

@unittest.skipUnless(c_functools, 'requires the C _functools module')
class TestPartialC(TestPartial, unittest.TestCase):
    if c_functools:
        partial = c_functools.partial

    class AllowPickle:
        def __enter__(self):
            return self
        def __exit__(self, type, value, tb):
            return False

    def test_attributes_unwritable(self):
        # attributes should not be writable
        p = self.partial(capture, 1, 2, a=10, b=20)
        self.assertRaises(AttributeError, setattr, p, 'func', map)
        self.assertRaises(AttributeError, setattr, p, 'args', (1, 2))
        self.assertRaises(AttributeError, setattr, p, 'keywords', dict(a=1, b=2))

        p = self.partial(hex)
        try:
            del p.__dict__
        except TypeError:
            pass
        else:
            self.fail('partial object allowed __dict__ to be deleted')

    def test_manually_adding_non_string_keyword(self):
        p = self.partial(capture)
        # Adding a non-string/unicode keyword to partial kwargs
        p.keywords[1234] = 'value'
        r = repr(p)
        self.assertIn('1234', r)
        self.assertIn("'value'", r)
        with self.assertRaises(TypeError):
            p()

    def test_keystr_replaces_value(self):
        p = self.partial(capture)

        class MutatesYourDict(object):
            def __str__(self):
                p.keywords[self] = ['sth2']
                return 'astr'

        # Replacing the value during key formatting should keep the original
        # value alive (at least long enough).
        p.keywords[MutatesYourDict()] = ['sth']
        r = repr(p)
        self.assertIn('astr', r)
        self.assertIn("['sth']", r)


class TestPartialPy(TestPartial, unittest.TestCase):
    partial = py_functools.partial

    class AllowPickle:
        def __init__(self):
            self._cm = replaced_module("functools", py_functools)
        def __enter__(self):
            return self._cm.__enter__()
        def __exit__(self, type, value, tb):
            return self._cm.__exit__(type, value, tb)

if c_functools:
    class CPartialSubclass(c_functools.partial):
        pass

class PyPartialSubclass(py_functools.partial):
    pass

@unittest.skipUnless(c_functools, 'requires the C _functools module')
class TestPartialCSubclass(TestPartialC):
    if c_functools:
        partial = CPartialSubclass

    # partial subclasses are not optimized for nested calls
    test_nested_optimization = None

class TestPartialPySubclass(TestPartialPy):
    partial = PyPartialSubclass

class TestPartialMethod(unittest.TestCase):

    class A(object):
        nothing = functools.partialmethod(capture)
        positional = functools.partialmethod(capture, 1)
        keywords = functools.partialmethod(capture, a=2)
        both = functools.partialmethod(capture, 3, b=4)
        spec_keywords = functools.partialmethod(capture, self=1, func=2)

        nested = functools.partialmethod(positional, 5)

        over_partial = functools.partialmethod(functools.partial(capture, c=6), 7)

        static = functools.partialmethod(staticmethod(capture), 8)
        cls = functools.partialmethod(classmethod(capture), d=9)

    a = A()

    def test_arg_combinations(self):
        self.assertEqual(self.a.nothing(), ((self.a,), {}))
        self.assertEqual(self.a.nothing(5), ((self.a, 5), {}))
        self.assertEqual(self.a.nothing(c=6), ((self.a,), {'c': 6}))
        self.assertEqual(self.a.nothing(5, c=6), ((self.a, 5), {'c': 6}))

        self.assertEqual(self.a.positional(), ((self.a, 1), {}))
        self.assertEqual(self.a.positional(5), ((self.a, 1, 5), {}))
        self.assertEqual(self.a.positional(c=6), ((self.a, 1), {'c': 6}))
        self.assertEqual(self.a.positional(5, c=6), ((self.a, 1, 5), {'c': 6}))

        self.assertEqual(self.a.keywords(), ((self.a,), {'a': 2}))
        self.assertEqual(self.a.keywords(5), ((self.a, 5), {'a': 2}))
        self.assertEqual(self.a.keywords(c=6), ((self.a,), {'a': 2, 'c': 6}))
        self.assertEqual(self.a.keywords(5, c=6), ((self.a, 5), {'a': 2, 'c': 6}))

        self.assertEqual(self.a.both(), ((self.a, 3), {'b': 4}))
        self.assertEqual(self.a.both(5), ((self.a, 3, 5), {'b': 4}))
        self.assertEqual(self.a.both(c=6), ((self.a, 3), {'b': 4, 'c': 6}))
        self.assertEqual(self.a.both(5, c=6), ((self.a, 3, 5), {'b': 4, 'c': 6}))

        self.assertEqual(self.A.both(self.a, 5, c=6), ((self.a, 3, 5), {'b': 4, 'c': 6}))

        self.assertEqual(self.a.spec_keywords(), ((self.a,), {'self': 1, 'func': 2}))

    def test_nested(self):
        self.assertEqual(self.a.nested(), ((self.a, 1, 5), {}))
        self.assertEqual(self.a.nested(6), ((self.a, 1, 5, 6), {}))
        self.assertEqual(self.a.nested(d=7), ((self.a, 1, 5), {'d': 7}))
        self.assertEqual(self.a.nested(6, d=7), ((self.a, 1, 5, 6), {'d': 7}))

        self.assertEqual(self.A.nested(self.a, 6, d=7), ((self.a, 1, 5, 6), {'d': 7}))

    def test_over_partial(self):
        self.assertEqual(self.a.over_partial(), ((self.a, 7), {'c': 6}))
        self.assertEqual(self.a.over_partial(5), ((self.a, 7, 5), {'c': 6}))
        self.assertEqual(self.a.over_partial(d=8), ((self.a, 7), {'c': 6, 'd': 8}))
        self.assertEqual(self.a.over_partial(5, d=8), ((self.a, 7, 5), {'c': 6, 'd': 8}))

        self.assertEqual(self.A.over_partial(self.a, 5, d=8), ((self.a, 7, 5), {'c': 6, 'd': 8}))

    def test_bound_method_introspection(self):
        obj = self.a
        self.assertIs(obj.both.__self__, obj)
        self.assertIs(obj.nested.__self__, obj)
        self.assertIs(obj.over_partial.__self__, obj)
        self.assertIs(obj.cls.__self__, self.A)
        self.assertIs(self.A.cls.__self__, self.A)

    def test_unbound_method_retrieval(self):
        obj = self.A
        self.assertFalse(hasattr(obj.both, "__self__"))
        self.assertFalse(hasattr(obj.nested, "__self__"))
        self.assertFalse(hasattr(obj.over_partial, "__self__"))
        self.assertFalse(hasattr(obj.static, "__self__"))
        self.assertFalse(hasattr(self.a.static, "__self__"))

    def test_descriptors(self):
        for obj in [self.A, self.a]:
            with self.subTest(obj=obj):
                self.assertEqual(obj.static(), ((8,), {}))
                self.assertEqual(obj.static(5), ((8, 5), {}))
                self.assertEqual(obj.static(d=8), ((8,), {'d': 8}))
                self.assertEqual(obj.static(5, d=8), ((8, 5), {'d': 8}))

                self.assertEqual(obj.cls(), ((self.A,), {'d': 9}))
                self.assertEqual(obj.cls(5), ((self.A, 5), {'d': 9}))
                self.assertEqual(obj.cls(c=8), ((self.A,), {'c': 8, 'd': 9}))
                self.assertEqual(obj.cls(5, c=8), ((self.A, 5), {'c': 8, 'd': 9}))

    def test_overriding_keywords(self):
        self.assertEqual(self.a.keywords(a=3), ((self.a,), {'a': 3}))
        self.assertEqual(self.A.keywords(self.a, a=3), ((self.a,), {'a': 3}))

    def test_invalid_args(self):
        with self.assertRaises(TypeError):
            class B(object):
                method = functools.partialmethod(None, 1)
        with self.assertRaises(TypeError):
            class B:
                method = functools.partialmethod()
        class B:
            method = functools.partialmethod(func=capture, a=1)
        b = B()
        self.assertEqual(b.method(2, x=3), ((b, 2), {'a': 1, 'x': 3}))

    def test_repr(self):
        self.assertEqual(repr(vars(self.A)['both']),
                         'functools.partialmethod({}, 3, b=4)'.format(capture))

    def test_abstract(self):
        class Abstract(abc.ABCMeta):

            @abc.abstractmethod
            def add(self, x, y):
                pass

            add5 = functools.partialmethod(add, 5)

        self.assertTrue(Abstract.add.__isabstractmethod__)
        self.assertTrue(Abstract.add5.__isabstractmethod__)

        for func in [self.A.static, self.A.cls, self.A.over_partial, self.A.nested, self.A.both]:
            self.assertFalse(getattr(func, '__isabstractmethod__', False))


class TestUpdateWrapper(unittest.TestCase):

    def check_wrapper(self, wrapper, wrapped,
                      assigned=functools.WRAPPER_ASSIGNMENTS,
                      updated=functools.WRAPPER_UPDATES):
        # Check attributes were assigned
        for name in assigned:
            self.assertIs(getattr(wrapper, name), getattr(wrapped, name))
        # Check attributes were updated
        for name in updated:
            wrapper_attr = getattr(wrapper, name)
            wrapped_attr = getattr(wrapped, name)
            for key in wrapped_attr:
                if name == "__dict__" and key == "__wrapped__":
                    # __wrapped__ is overwritten by the update code
                    continue
                self.assertIs(wrapped_attr[key], wrapper_attr[key])
        # Check __wrapped__
        self.assertIs(wrapper.__wrapped__, wrapped)


    def _default_update(self):
        def f(a:'This is a new annotation'):
            """This is a test"""
            pass
        f.attr = 'This is also a test'
        f.__wrapped__ = "This is a bald faced lie"
        def wrapper(b:'This is the prior annotation'):
            pass
        functools.update_wrapper(wrapper, f)
        return wrapper, f

    def test_default_update(self):
        wrapper, f = self._default_update()
        self.check_wrapper(wrapper, f)
        self.assertIs(wrapper.__wrapped__, f)
        self.assertEqual(wrapper.__name__, 'f')
        self.assertEqual(wrapper.__qualname__, f.__qualname__)
        self.assertEqual(wrapper.attr, 'This is also a test')
        self.assertEqual(wrapper.__annotations__['a'], 'This is a new annotation')
        self.assertNotIn('b', wrapper.__annotations__)

    @unittest.skipIf(sys.flags.optimize >= 2,
                     "Docstrings are omitted with -O2 and above")
    def test_default_update_doc(self):
        wrapper, f = self._default_update()
        self.assertEqual(wrapper.__doc__, 'This is a test')

    def test_no_update(self):
        def f():
            """This is a test"""
            pass
        f.attr = 'This is also a test'
        def wrapper():
            pass
        functools.update_wrapper(wrapper, f, (), ())
        self.check_wrapper(wrapper, f, (), ())
        self.assertEqual(wrapper.__name__, 'wrapper')
        self.assertNotEqual(wrapper.__qualname__, f.__qualname__)
        self.assertEqual(wrapper.__doc__, None)
        self.assertEqual(wrapper.__annotations__, {})
        self.assertFalse(hasattr(wrapper, 'attr'))

    def test_selective_update(self):
        def f():
            pass
        f.attr = 'This is a different test'
        f.dict_attr = dict(a=1, b=2, c=3)
        def wrapper():
            pass
        wrapper.dict_attr = {}
        assign = ('attr',)
        update = ('dict_attr',)
        functools.update_wrapper(wrapper, f, assign, update)
        self.check_wrapper(wrapper, f, assign, update)
        self.assertEqual(wrapper.__name__, 'wrapper')
        self.assertNotEqual(wrapper.__qualname__, f.__qualname__)
        self.assertEqual(wrapper.__doc__, None)
        self.assertEqual(wrapper.attr, 'This is a different test')
        self.assertEqual(wrapper.dict_attr, f.dict_attr)

    def test_missing_attributes(self):
        def f():
            pass
        def wrapper():
            pass
        wrapper.dict_attr = {}
        assign = ('attr',)
        update = ('dict_attr',)
        # Missing attributes on wrapped object are ignored
        functools.update_wrapper(wrapper, f, assign, update)
        self.assertNotIn('attr', wrapper.__dict__)
        self.assertEqual(wrapper.dict_attr, {})
        # Wrapper must have expected attributes for updating
        del wrapper.dict_attr
        with self.assertRaises(AttributeError):
            functools.update_wrapper(wrapper, f, assign, update)
        wrapper.dict_attr = 1
        with self.assertRaises(AttributeError):
            functools.update_wrapper(wrapper, f, assign, update)

    @support.requires_docstrings
    @unittest.skipIf(sys.flags.optimize >= 2,
                     "Docstrings are omitted with -O2 and above")
    def test_builtin_update(self):
        # Test for bug #1576241
        def wrapper():
            pass
        functools.update_wrapper(wrapper, max)
        self.assertEqual(wrapper.__name__, 'max')
        self.assertTrue(wrapper.__doc__.startswith('max('))
        self.assertEqual(wrapper.__annotations__, {})


class TestWraps(TestUpdateWrapper):

    def _default_update(self):
        def f():
            """This is a test"""
            pass
        f.attr = 'This is also a test'
        f.__wrapped__ = "This is still a bald faced lie"
        @functools.wraps(f)
        def wrapper():
            pass
        return wrapper, f

    def test_default_update(self):
        wrapper, f = self._default_update()
        self.check_wrapper(wrapper, f)
        self.assertEqual(wrapper.__name__, 'f')
        self.assertEqual(wrapper.__qualname__, f.__qualname__)
        self.assertEqual(wrapper.attr, 'This is also a test')

    @unittest.skipIf(sys.flags.optimize >= 2,
                     "Docstrings are omitted with -O2 and above")
    def test_default_update_doc(self):
        wrapper, _ = self._default_update()
        self.assertEqual(wrapper.__doc__, 'This is a test')

    def test_no_update(self):
        def f():
            """This is a test"""
            pass
        f.attr = 'This is also a test'
        @functools.wraps(f, (), ())
        def wrapper():
            pass
        self.check_wrapper(wrapper, f, (), ())
        self.assertEqual(wrapper.__name__, 'wrapper')
        self.assertNotEqual(wrapper.__qualname__, f.__qualname__)
        self.assertEqual(wrapper.__doc__, None)
        self.assertFalse(hasattr(wrapper, 'attr'))

    def test_selective_update(self):
        def f():
            pass
        f.attr = 'This is a different test'
        f.dict_attr = dict(a=1, b=2, c=3)
        def add_dict_attr(f):
            f.dict_attr = {}
            return f
        assign = ('attr',)
        update = ('dict_attr',)
        @functools.wraps(f, assign, update)
        @add_dict_attr
        def wrapper():
            pass
        self.check_wrapper(wrapper, f, assign, update)
        self.assertEqual(wrapper.__name__, 'wrapper')
        self.assertNotEqual(wrapper.__qualname__, f.__qualname__)
        self.assertEqual(wrapper.__doc__, None)
        self.assertEqual(wrapper.attr, 'This is a different test')
        self.assertEqual(wrapper.dict_attr, f.dict_attr)

@unittest.skipUnless(c_functools, 'requires the C _functools module')
class TestReduce(unittest.TestCase):
    if c_functools:
        func = c_functools.reduce

    def test_reduce(self):
        class Squares:
            def __init__(self, max):
                self.max = max
                self.sofar = []

            def __len__(self):
                return len(self.sofar)

            def __getitem__(self, i):
                if not 0 <= i < self.max: raise IndexError
                n = len(self.sofar)
                while n <= i:
                    self.sofar.append(n*n)
                    n += 1
                return self.sofar[i]
        def add(x, y):
            return x + y
        self.assertEqual(self.func(add, ['a', 'b', 'c'], ''), 'abc')
        self.assertEqual(
            self.func(add, [['a', 'c'], [], ['d', 'w']], []),
            ['a','c','d','w']
        )
        self.assertEqual(self.func(lambda x, y: x*y, range(2,8), 1), 5040)
        self.assertEqual(
            self.func(lambda x, y: x*y, range(2,21), 1),
            2432902008176640000
        )
        self.assertEqual(self.func(add, Squares(10)), 285)
        self.assertEqual(self.func(add, Squares(10), 0), 285)
        self.assertEqual(self.func(add, Squares(0), 0), 0)
        self.assertRaises(TypeError, self.func)
        self.assertRaises(TypeError, self.func, 42, 42)
        self.assertRaises(TypeError, self.func, 42, 42, 42)
        self.assertEqual(self.func(42, "1"), "1") # func is never called with one item
        self.assertEqual(self.func(42, "", "1"), "1") # func is never called with one item
        self.assertRaises(TypeError, self.func, 42, (42, 42))
        self.assertRaises(TypeError, self.func, add, []) # arg 2 must not be empty sequence with no initial value
        self.assertRaises(TypeError, self.func, add, "")
        self.assertRaises(TypeError, self.func, add, ())
        self.assertRaises(TypeError, self.func, add, object())

        class TestFailingIter:
            def __iter__(self):
                raise RuntimeError
        self.assertRaises(RuntimeError, self.func, add, TestFailingIter())

        self.assertEqual(self.func(add, [], None), None)
        self.assertEqual(self.func(add, [], 42), 42)

        class BadSeq:
            def __getitem__(self, index):
                raise ValueError
        self.assertRaises(ValueError, self.func, 42, BadSeq())

    # Test reduce()'s use of iterators.
    def test_iterator_usage(self):
        class SequenceClass:
            def __init__(self, n):
                self.n = n
            def __getitem__(self, i):
                if 0 <= i < self.n:
                    return i
                else:
                    raise IndexError

        from operator import add
        self.assertEqual(self.func(add, SequenceClass(5)), 10)
        self.assertEqual(self.func(add, SequenceClass(5), 42), 52)
        self.assertRaises(TypeError, self.func, add, SequenceClass(0))
        self.assertEqual(self.func(add, SequenceClass(0), 42), 42)
        self.assertEqual(self.func(add, SequenceClass(1)), 0)
        self.assertEqual(self.func(add, SequenceClass(1), 42), 42)

        d = {"one": 1, "two": 2, "three": 3}
        self.assertEqual(self.func(add, d), "".join(d.keys()))


class TestCmpToKey:

    def test_cmp_to_key(self):
        def cmp1(x, y):
            return (x > y) - (x < y)
        key = self.cmp_to_key(cmp1)
        self.assertEqual(key(3), key(3))
        self.assertGreater(key(3), key(1))
        self.assertGreaterEqual(key(3), key(3))

        def cmp2(x, y):
            return int(x) - int(y)
        key = self.cmp_to_key(cmp2)
        self.assertEqual(key(4.0), key('4'))
        self.assertLess(key(2), key('35'))
        self.assertLessEqual(key(2), key('35'))
        self.assertNotEqual(key(2), key('35'))

    def test_cmp_to_key_arguments(self):
        def cmp1(x, y):
            return (x > y) - (x < y)
        key = self.cmp_to_key(mycmp=cmp1)
        self.assertEqual(key(obj=3), key(obj=3))
        self.assertGreater(key(obj=3), key(obj=1))
        with self.assertRaises((TypeError, AttributeError)):
            key(3) > 1    # rhs is not a K object
        with self.assertRaises((TypeError, AttributeError)):
            1 < key(3)    # lhs is not a K object
        with self.assertRaises(TypeError):
            key = self.cmp_to_key()             # too few args
        with self.assertRaises(TypeError):
            key = self.cmp_to_key(cmp1, None)   # too many args
        key = self.cmp_to_key(cmp1)
        with self.assertRaises(TypeError):
            key()                                    # too few args
        with self.assertRaises(TypeError):
            key(None, None)                          # too many args

    def test_bad_cmp(self):
        def cmp1(x, y):
            raise ZeroDivisionError
        key = self.cmp_to_key(cmp1)
        with self.assertRaises(ZeroDivisionError):
            key(3) > key(1)

        class BadCmp:
            def __lt__(self, other):
                raise ZeroDivisionError
        def cmp1(x, y):
            return BadCmp()
        with self.assertRaises(ZeroDivisionError):
            key(3) > key(1)

    def test_obj_field(self):
        def cmp1(x, y):
            return (x > y) - (x < y)
        key = self.cmp_to_key(mycmp=cmp1)
        self.assertEqual(key(50).obj, 50)

    def test_sort_int(self):
        def mycmp(x, y):
            return y - x
        self.assertEqual(sorted(range(5), key=self.cmp_to_key(mycmp)),
                         [4, 3, 2, 1, 0])

    def test_sort_int_str(self):
        def mycmp(x, y):
            x, y = int(x), int(y)
            return (x > y) - (x < y)
        values = [5, '3', 7, 2, '0', '1', 4, '10', 1]
        values = sorted(values, key=self.cmp_to_key(mycmp))
        self.assertEqual([int(value) for value in values],
                         [0, 1, 1, 2, 3, 4, 5, 7, 10])

    def test_hash(self):
        def mycmp(x, y):
            return y - x
        key = self.cmp_to_key(mycmp)
        k = key(10)
        self.assertRaises(TypeError, hash, k)
        self.assertNotIsInstance(k, collections.abc.Hashable)


@unittest.skipUnless(c_functools, 'requires the C _functools module')
class TestCmpToKeyC(TestCmpToKey, unittest.TestCase):
    if c_functools:
        cmp_to_key = c_functools.cmp_to_key


class TestCmpToKeyPy(TestCmpToKey, unittest.TestCase):
    cmp_to_key = staticmethod(py_functools.cmp_to_key)


class TestTotalOrdering(unittest.TestCase):

    def test_total_ordering_lt(self):
        @functools.total_ordering
        class A:
            def __init__(self, value):
                self.value = value
            def __lt__(self, other):
                return self.value < other.value
            def __eq__(self, other):
                return self.value == other.value
        self.assertTrue(A(1) < A(2))
        self.assertTrue(A(2) > A(1))
        self.assertTrue(A(1) <= A(2))
        self.assertTrue(A(2) >= A(1))
        self.assertTrue(A(2) <= A(2))
        self.assertTrue(A(2) >= A(2))
        self.assertFalse(A(1) > A(2))

    def test_total_ordering_le(self):
        @functools.total_ordering
        class A:
            def __init__(self, value):
                self.value = value
            def __le__(self, other):
                return self.value <= other.value
            def __eq__(self, other):
                return self.value == other.value
        self.assertTrue(A(1) < A(2))
        self.assertTrue(A(2) > A(1))
        self.assertTrue(A(1) <= A(2))
        self.assertTrue(A(2) >= A(1))
        self.assertTrue(A(2) <= A(2))
        self.assertTrue(A(2) >= A(2))
        self.assertFalse(A(1) >= A(2))

    def test_total_ordering_gt(self):
        @functools.total_ordering
        class A:
            def __init__(self, value):
                self.value = value
            def __gt__(self, other):
                return self.value > other.value
            def __eq__(self, other):
                return self.value == other.value
        self.assertTrue(A(1) < A(2))
        self.assertTrue(A(2) > A(1))
        self.assertTrue(A(1) <= A(2))
        self.assertTrue(A(2) >= A(1))
        self.assertTrue(A(2) <= A(2))
        self.assertTrue(A(2) >= A(2))
        self.assertFalse(A(2) < A(1))

    def test_total_ordering_ge(self):
        @functools.total_ordering
        class A:
            def __init__(self, value):
                self.value = value
            def __ge__(self, other):
                return self.value >= other.value
            def __eq__(self, other):
                return self.value == other.value
        self.assertTrue(A(1) < A(2))
        self.assertTrue(A(2) > A(1))
        self.assertTrue(A(1) <= A(2))
        self.assertTrue(A(2) >= A(1))
        self.assertTrue(A(2) <= A(2))
        self.assertTrue(A(2) >= A(2))
        self.assertFalse(A(2) <= A(1))

    def test_total_ordering_no_overwrite(self):
        # new methods should not overwrite existing
        @functools.total_ordering
        class A(int):
            pass
        self.assertTrue(A(1) < A(2))
        self.assertTrue(A(2) > A(1))
        self.assertTrue(A(1) <= A(2))
        self.assertTrue(A(2) >= A(1))
        self.assertTrue(A(2) <= A(2))
        self.assertTrue(A(2) >= A(2))

    def test_no_operations_defined(self):
        with self.assertRaises(ValueError):
            @functools.total_ordering
            class A:
                pass

    def test_type_error_when_not_implemented(self):
        # bug 10042; ensure stack overflow does not occur
        # when decorated types return NotImplemented
        @functools.total_ordering
        class ImplementsLessThan:
            def __init__(self, value):
                self.value = value
            def __eq__(self, other):
                if isinstance(other, ImplementsLessThan):
                    return self.value == other.value
                return False
            def __lt__(self, other):
                if isinstance(other, ImplementsLessThan):
                    return self.value < other.value
                return NotImplemented

        @functools.total_ordering
        class ImplementsGreaterThan:
            def __init__(self, value):
                self.value = value
            def __eq__(self, other):
                if isinstance(other, ImplementsGreaterThan):
                    return self.value == other.value
                return False
            def __gt__(self, other):
                if isinstance(other, ImplementsGreaterThan):
                    return self.value > other.value
                return NotImplemented

        @functools.total_ordering
        class ImplementsLessThanEqualTo:
            def __init__(self, value):
                self.value = value
            def __eq__(self, other):
                if isinstance(other, ImplementsLessThanEqualTo):
                    return self.value == other.value
                return False
            def __le__(self, other):
                if isinstance(other, ImplementsLessThanEqualTo):
                    return self.value <= other.value
                return NotImplemented

        @functools.total_ordering
        class ImplementsGreaterThanEqualTo:
            def __init__(self, value):
                self.value = value
            def __eq__(self, other):
                if isinstance(other, ImplementsGreaterThanEqualTo):
                    return self.value == other.value
                return False
            def __ge__(self, other):
                if isinstance(other, ImplementsGreaterThanEqualTo):
                    return self.value >= other.value
                return NotImplemented

        @functools.total_ordering
        class ComparatorNotImplemented:
            def __init__(self, value):
                self.value = value
            def __eq__(self, other):
                if isinstance(other, ComparatorNotImplemented):
                    return self.value == other.value
                return False
            def __lt__(self, other):
                return NotImplemented

        with self.subTest("LT < 1"), self.assertRaises(TypeError):
            ImplementsLessThan(-1) < 1

        with self.subTest("LT < LE"), self.assertRaises(TypeError):
            ImplementsLessThan(0) < ImplementsLessThanEqualTo(0)

        with self.subTest("LT < GT"), self.assertRaises(TypeError):
            ImplementsLessThan(1) < ImplementsGreaterThan(1)

        with self.subTest("LE <= LT"), self.assertRaises(TypeError):
            ImplementsLessThanEqualTo(2) <= ImplementsLessThan(2)

        with self.subTest("LE <= GE"), self.assertRaises(TypeError):
            ImplementsLessThanEqualTo(3) <= ImplementsGreaterThanEqualTo(3)

        with self.subTest("GT > GE"), self.assertRaises(TypeError):
            ImplementsGreaterThan(4) > ImplementsGreaterThanEqualTo(4)

        with self.subTest("GT > LT"), self.assertRaises(TypeError):
            ImplementsGreaterThan(5) > ImplementsLessThan(5)

        with self.subTest("GE >= GT"), self.assertRaises(TypeError):
            ImplementsGreaterThanEqualTo(6) >= ImplementsGreaterThan(6)

        with self.subTest("GE >= LE"), self.assertRaises(TypeError):
            ImplementsGreaterThanEqualTo(7) >= ImplementsLessThanEqualTo(7)

        with self.subTest("GE when equal"):
            a = ComparatorNotImplemented(8)
            b = ComparatorNotImplemented(8)
            self.assertEqual(a, b)
            with self.assertRaises(TypeError):
                a >= b

        with self.subTest("LE when equal"):
            a = ComparatorNotImplemented(9)
            b = ComparatorNotImplemented(9)
            self.assertEqual(a, b)
            with self.assertRaises(TypeError):
                a <= b

    def test_pickle(self):
        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
            for name in '__lt__', '__gt__', '__le__', '__ge__':
                with self.subTest(method=name, proto=proto):
                    method = getattr(Orderable_LT, name)
                    method_copy = pickle.loads(pickle.dumps(method, proto))
                    self.assertIs(method_copy, method)

@functools.total_ordering
class Orderable_LT:
    def __init__(self, value):
        self.value = value
    def __lt__(self, other):
        return self.value < other.value
    def __eq__(self, other):
        return self.value == other.value


class TestLRU:

    def test_lru(self):
        def orig(x, y):
            return 3 * x + y
        f = self.module.lru_cache(maxsize=20)(orig)
        hits, misses, maxsize, currsize = f.cache_info()
        self.assertEqual(maxsize, 20)
        self.assertEqual(currsize, 0)
        self.assertEqual(hits, 0)
        self.assertEqual(misses, 0)

        domain = range(5)
        for i in range(1000):
            x, y = choice(domain), choice(domain)
            actual = f(x, y)
            expected = orig(x, y)
            self.assertEqual(actual, expected)
        hits, misses, maxsize, currsize = f.cache_info()
        self.assertTrue(hits > misses)
        self.assertEqual(hits + misses, 1000)
        self.assertEqual(currsize, 20)

        f.cache_clear()   # test clearing
        hits, misses, maxsize, currsize = f.cache_info()
        self.assertEqual(hits, 0)
        self.assertEqual(misses, 0)
        self.assertEqual(currsize, 0)
        f(x, y)
        hits, misses, maxsize, currsize = f.cache_info()
        self.assertEqual(hits, 0)
        self.assertEqual(misses, 1)
        self.assertEqual(currsize, 1)

        # Test bypassing the cache
        self.assertIs(f.__wrapped__, orig)
        f.__wrapped__(x, y)
        hits, misses, maxsize, currsize = f.cache_info()
        self.assertEqual(hits, 0)
        self.assertEqual(misses, 1)
        self.assertEqual(currsize, 1)

        # test size zero (which means "never-cache")
        @self.module.lru_cache(0)
        def f():
            nonlocal f_cnt
            f_cnt += 1
            return 20
        self.assertEqual(f.cache_info().maxsize, 0)
        f_cnt = 0
        for i in range(5):
            self.assertEqual(f(), 20)
        self.assertEqual(f_cnt, 5)
        hits, misses, maxsize, currsize = f.cache_info()
        self.assertEqual(hits, 0)
        self.assertEqual(misses, 5)
        self.assertEqual(currsize, 0)

        # test size one
        @self.module.lru_cache(1)
        def f():
            nonlocal f_cnt
            f_cnt += 1
            return 20
        self.assertEqual(f.cache_info().maxsize, 1)
        f_cnt = 0
        for i in range(5):
            self.assertEqual(f(), 20)
        self.assertEqual(f_cnt, 1)
        hits, misses, maxsize, currsize = f.cache_info()
        self.assertEqual(hits, 4)
        self.assertEqual(misses, 1)
        self.assertEqual(currsize, 1)

        # test size two
        @self.module.lru_cache(2)
        def f(x):
            nonlocal f_cnt
            f_cnt += 1
            return x*10
        self.assertEqual(f.cache_info().maxsize, 2)
        f_cnt = 0
        for x in 7, 9, 7, 9, 7, 9, 8, 8, 8, 9, 9, 9, 8, 8, 8, 7:
            #    *  *              *                          *
            self.assertEqual(f(x), x*10)
        self.assertEqual(f_cnt, 4)
        hits, misses, maxsize, currsize = f.cache_info()
        self.assertEqual(hits, 12)
        self.assertEqual(misses, 4)
        self.assertEqual(currsize, 2)

    def test_lru_bug_35780(self):
        # C version of the lru_cache was not checking to see if
        # the user function call has already modified the cache
        # (this arises in recursive calls and in multi-threading).
        # This cause the cache to have orphan links not referenced
        # by the cache dictionary.

        once = True                 # Modified by f(x) below

        @self.module.lru_cache(maxsize=10)
        def f(x):
            nonlocal once
            rv = f'.{x}.'
            if x == 20 and once:
                once = False
                rv = f(x)
            return rv

        # Fill the cache
        for x in range(15):
            self.assertEqual(f(x), f'.{x}.')
        self.assertEqual(f.cache_info().currsize, 10)

        # Make a recursive call and make sure the cache remains full
        self.assertEqual(f(20), '.20.')
        self.assertEqual(f.cache_info().currsize, 10)

    def test_lru_hash_only_once(self):
        # To protect against weird reentrancy bugs and to improve
        # efficiency when faced with slow __hash__ methods, the
        # LRU cache guarantees that it will only call __hash__
        # only once per use as an argument to the cached function.

        @self.module.lru_cache(maxsize=1)
        def f(x, y):
            return x * 3 + y

        # Simulate the integer 5
        mock_int = unittest.mock.Mock()
        mock_int.__mul__ = unittest.mock.Mock(return_value=15)
        mock_int.__hash__ = unittest.mock.Mock(return_value=999)

        # Add to cache:  One use as an argument gives one call
        self.assertEqual(f(mock_int, 1), 16)
        self.assertEqual(mock_int.__hash__.call_count, 1)
        self.assertEqual(f.cache_info(), (0, 1, 1, 1))

        # Cache hit: One use as an argument gives one additional call
        self.assertEqual(f(mock_int, 1), 16)
        self.assertEqual(mock_int.__hash__.call_count, 2)
        self.assertEqual(f.cache_info(), (1, 1, 1, 1))

        # Cache eviction: No use as an argument gives no additional call
        self.assertEqual(f(6, 2), 20)
        self.assertEqual(mock_int.__hash__.call_count, 2)
        self.assertEqual(f.cache_info(), (1, 2, 1, 1))

        # Cache miss: One use as an argument gives one additional call
        self.assertEqual(f(mock_int, 1), 16)
        self.assertEqual(mock_int.__hash__.call_count, 3)
        self.assertEqual(f.cache_info(), (1, 3, 1, 1))

    def test_lru_reentrancy_with_len(self):
        # Test to make sure the LRU cache code isn't thrown-off by
        # caching the built-in len() function.  Since len() can be
        # cached, we shouldn't use it inside the lru code itself.
        old_len = builtins.len
        try:
            builtins.len = self.module.lru_cache(4)(len)
            for i in [0, 0, 1, 2, 3, 3, 4, 5, 6, 1, 7, 2, 1]:
                self.assertEqual(len('abcdefghijklmn'[:i]), i)
        finally:
            builtins.len = old_len

    def test_lru_star_arg_handling(self):
        # Test regression that arose in ea064ff3c10f
        @functools.lru_cache()
        def f(*args):
            return args

        self.assertEqual(f(1, 2), (1, 2))
        self.assertEqual(f((1, 2)), ((1, 2),))

    def test_lru_type_error(self):
        # Regression test for issue #28653.
        # lru_cache was leaking when one of the arguments
        # wasn't cacheable.

        @functools.lru_cache(maxsize=None)
        def infinite_cache(o):
            pass

        @functools.lru_cache(maxsize=10)
        def limited_cache(o):
            pass

        with self.assertRaises(TypeError):
            infinite_cache([])

        with self.assertRaises(TypeError):
            limited_cache([])

    def test_lru_with_maxsize_none(self):
        @self.module.lru_cache(maxsize=None)
        def fib(n):
            if n < 2:
                return n
            return fib(n-1) + fib(n-2)
        self.assertEqual([fib(n) for n in range(16)],
            [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610])
        self.assertEqual(fib.cache_info(),
            self.module._CacheInfo(hits=28, misses=16, maxsize=None, currsize=16))
        fib.cache_clear()
        self.assertEqual(fib.cache_info(),
            self.module._CacheInfo(hits=0, misses=0, maxsize=None, currsize=0))

    def test_lru_with_maxsize_negative(self):
        @self.module.lru_cache(maxsize=-10)
        def eq(n):
            return n
        for i in (0, 1):
            self.assertEqual([eq(n) for n in range(150)], list(range(150)))
        self.assertEqual(eq.cache_info(),
            self.module._CacheInfo(hits=0, misses=300, maxsize=0, currsize=0))

    def test_lru_with_exceptions(self):
        # Verify that user_function exceptions get passed through without
        # creating a hard-to-read chained exception.
        # http://bugs.python.org/issue13177
        for maxsize in (None, 128):
            @self.module.lru_cache(maxsize)
            def func(i):
                return 'abc'[i]
            self.assertEqual(func(0), 'a')
            with self.assertRaises(IndexError) as cm:
                func(15)
            self.assertIsNone(cm.exception.__context__)
            # Verify that the previous exception did not result in a cached entry
            with self.assertRaises(IndexError):
                func(15)

    def test_lru_with_types(self):
        for maxsize in (None, 128):
            @self.module.lru_cache(maxsize=maxsize, typed=True)
            def square(x):
                return x * x
            self.assertEqual(square(3), 9)
            self.assertEqual(type(square(3)), type(9))
            self.assertEqual(square(3.0), 9.0)
            self.assertEqual(type(square(3.0)), type(9.0))
            self.assertEqual(square(x=3), 9)
            self.assertEqual(type(square(x=3)), type(9))
            self.assertEqual(square(x=3.0), 9.0)
            self.assertEqual(type(square(x=3.0)), type(9.0))
            self.assertEqual(square.cache_info().hits, 4)
            self.assertEqual(square.cache_info().misses, 4)

    def test_lru_with_keyword_args(self):
        @self.module.lru_cache()
        def fib(n):
            if n < 2:
                return n
            return fib(n=n-1) + fib(n=n-2)
        self.assertEqual(
            [fib(n=number) for number in range(16)],
            [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610]
        )
        self.assertEqual(fib.cache_info(),
            self.module._CacheInfo(hits=28, misses=16, maxsize=128, currsize=16))
        fib.cache_clear()
        self.assertEqual(fib.cache_info(),
            self.module._CacheInfo(hits=0, misses=0, maxsize=128, currsize=0))

    def test_lru_with_keyword_args_maxsize_none(self):
        @self.module.lru_cache(maxsize=None)
        def fib(n):
            if n < 2:
                return n
            return fib(n=n-1) + fib(n=n-2)
        self.assertEqual([fib(n=number) for number in range(16)],
            [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610])
        self.assertEqual(fib.cache_info(),
            self.module._CacheInfo(hits=28, misses=16, maxsize=None, currsize=16))
        fib.cache_clear()
        self.assertEqual(fib.cache_info(),
            self.module._CacheInfo(hits=0, misses=0, maxsize=None, currsize=0))

    def test_kwargs_order(self):
        # PEP 468: Preserving Keyword Argument Order
        @self.module.lru_cache(maxsize=10)
        def f(**kwargs):
            return list(kwargs.items())
        self.assertEqual(f(a=1, b=2), [('a', 1), ('b', 2)])
        self.assertEqual(f(b=2, a=1), [('b', 2), ('a', 1)])
        self.assertEqual(f.cache_info(),
            self.module._CacheInfo(hits=0, misses=2, maxsize=10, currsize=2))

    def test_lru_cache_decoration(self):
        def f(zomg: 'zomg_annotation'):
            """f doc string"""
            return 42
        g = self.module.lru_cache()(f)
        for attr in self.module.WRAPPER_ASSIGNMENTS:
            self.assertEqual(getattr(g, attr), getattr(f, attr))

    def test_lru_cache_threaded(self):
        n, m = 5, 11
        def orig(x, y):
            return 3 * x + y
        f = self.module.lru_cache(maxsize=n*m)(orig)
        hits, misses, maxsize, currsize = f.cache_info()
        self.assertEqual(currsize, 0)

        start = threading.Event()
        def full(k):
            start.wait(10)
            for _ in range(m):
                self.assertEqual(f(k, 0), orig(k, 0))

        def clear():
            start.wait(10)
            for _ in range(2*m):
                f.cache_clear()

        orig_si = sys.getswitchinterval()
        support.setswitchinterval(1e-6)
        try:
            # create n threads in order to fill cache
            threads = [threading.Thread(target=full, args=[k])
                       for k in range(n)]
            with support.start_threads(threads):
                start.set()

            hits, misses, maxsize, currsize = f.cache_info()
            if self.module is py_functools:
                # XXX: Why can be not equal?
                self.assertLessEqual(misses, n)
                self.assertLessEqual(hits, m*n - misses)
            else:
                self.assertEqual(misses, n)
                self.assertEqual(hits, m*n - misses)
            self.assertEqual(currsize, n)

            # create n threads in order to fill cache and 1 to clear it
            threads = [threading.Thread(target=clear)]
            threads += [threading.Thread(target=full, args=[k])
                        for k in range(n)]
            start.clear()
            with support.start_threads(threads):
                start.set()
        finally:
            sys.setswitchinterval(orig_si)

    def test_lru_cache_threaded2(self):
        # Simultaneous call with the same arguments
        n, m = 5, 7
        start = threading.Barrier(n+1)
        pause = threading.Barrier(n+1)
        stop = threading.Barrier(n+1)
        @self.module.lru_cache(maxsize=m*n)
        def f(x):
            pause.wait(10)
            return 3 * x
        self.assertEqual(f.cache_info(), (0, 0, m*n, 0))
        def test():
            for i in range(m):
                start.wait(10)
                self.assertEqual(f(i), 3 * i)
                stop.wait(10)
        threads = [threading.Thread(target=test) for k in range(n)]
        with support.start_threads(threads):
            for i in range(m):
                start.wait(10)
                stop.reset()
                pause.wait(10)
                start.reset()
                stop.wait(10)
                pause.reset()
                self.assertEqual(f.cache_info(), (0, (i+1)*n, m*n, i+1))

    def test_lru_cache_threaded3(self):
        @self.module.lru_cache(maxsize=2)
        def f(x):
            time.sleep(.01)
            return 3 * x
        def test(i, x):
            with self.subTest(thread=i):
                self.assertEqual(f(x), 3 * x, i)
        threads = [threading.Thread(target=test, args=(i, v))
                   for i, v in enumerate([1, 2, 2, 3, 2])]
        with support.start_threads(threads):
            pass

    def test_need_for_rlock(self):
        # This will deadlock on an LRU cache that uses a regular lock

        @self.module.lru_cache(maxsize=10)
        def test_func(x):
            'Used to demonstrate a reentrant lru_cache call within a single thread'
            return x

        class DoubleEq:
            'Demonstrate a reentrant lru_cache call within a single thread'
            def __init__(self, x):
                self.x = x
            def __hash__(self):
                return self.x
            def __eq__(self, other):
                if self.x == 2:
                    test_func(DoubleEq(1))
                return self.x == other.x

        test_func(DoubleEq(1))                      # Load the cache
        test_func(DoubleEq(2))                      # Load the cache
        self.assertEqual(test_func(DoubleEq(2)),    # Trigger a re-entrant __eq__ call
                         DoubleEq(2))               # Verify the correct return value

    def test_early_detection_of_bad_call(self):
        # Issue #22184
        with self.assertRaises(TypeError):
            @functools.lru_cache
            def f():
                pass

    def test_lru_method(self):
        class X(int):
            f_cnt = 0
            @self.module.lru_cache(2)
            def f(self, x):
                self.f_cnt += 1
                return x*10+self
        a = X(5)
        b = X(5)
        c = X(7)
        self.assertEqual(X.f.cache_info(), (0, 0, 2, 0))

        for x in 1, 2, 2, 3, 1, 1, 1, 2, 3, 3:
            self.assertEqual(a.f(x), x*10 + 5)
        self.assertEqual((a.f_cnt, b.f_cnt, c.f_cnt), (6, 0, 0))
        self.assertEqual(X.f.cache_info(), (4, 6, 2, 2))

        for x in 1, 2, 1, 1, 1, 1, 3, 2, 2, 2:
            self.assertEqual(b.f(x), x*10 + 5)
        self.assertEqual((a.f_cnt, b.f_cnt, c.f_cnt), (6, 4, 0))
        self.assertEqual(X.f.cache_info(), (10, 10, 2, 2))

        for x in 2, 1, 1, 1, 1, 2, 1, 3, 2, 1:
            self.assertEqual(c.f(x), x*10 + 7)
        self.assertEqual((a.f_cnt, b.f_cnt, c.f_cnt), (6, 4, 5))
        self.assertEqual(X.f.cache_info(), (15, 15, 2, 2))

        self.assertEqual(a.f.cache_info(), X.f.cache_info())
        self.assertEqual(b.f.cache_info(), X.f.cache_info())
        self.assertEqual(c.f.cache_info(), X.f.cache_info())

    def test_pickle(self):
        cls = self.__class__
        for f in cls.cached_func[0], cls.cached_meth, cls.cached_staticmeth:
            for proto in range(pickle.HIGHEST_PROTOCOL + 1):
                with self.subTest(proto=proto, func=f):
                    f_copy = pickle.loads(pickle.dumps(f, proto))
                    self.assertIs(f_copy, f)

    def test_copy(self):
        cls = self.__class__
        def orig(x, y):
            return 3 * x + y
        part = self.module.partial(orig, 2)
        funcs = (cls.cached_func[0], cls.cached_meth, cls.cached_staticmeth,
                 self.module.lru_cache(2)(part))
        for f in funcs:
            with self.subTest(func=f):
                f_copy = copy.copy(f)
                self.assertIs(f_copy, f)

    def test_deepcopy(self):
        cls = self.__class__
        def orig(x, y):
            return 3 * x + y
        part = self.module.partial(orig, 2)
        funcs = (cls.cached_func[0], cls.cached_meth, cls.cached_staticmeth,
                 self.module.lru_cache(2)(part))
        for f in funcs:
            with self.subTest(func=f):
                f_copy = copy.deepcopy(f)
                self.assertIs(f_copy, f)


@py_functools.lru_cache()
def py_cached_func(x, y):
    return 3 * x + y

@c_functools.lru_cache()
def c_cached_func(x, y):
    return 3 * x + y


class TestLRUPy(TestLRU, unittest.TestCase):
    module = py_functools
    cached_func = py_cached_func,

    @module.lru_cache()
    def cached_meth(self, x, y):
        return 3 * x + y

    @staticmethod
    @module.lru_cache()
    def cached_staticmeth(x, y):
        return 3 * x + y


class TestLRUC(TestLRU, unittest.TestCase):
    module = c_functools
    cached_func = c_cached_func,

    @module.lru_cache()
    def cached_meth(self, x, y):
        return 3 * x + y

    @staticmethod
    @module.lru_cache()
    def cached_staticmeth(x, y):
        return 3 * x + y


class TestSingleDispatch(unittest.TestCase):
    def test_simple_overloads(self):
        @functools.singledispatch
        def g(obj):
            return "base"
        def g_int(i):
            return "integer"
        g.register(int, g_int)
        self.assertEqual(g("str"), "base")
        self.assertEqual(g(1), "integer")
        self.assertEqual(g([1,2,3]), "base")

    def test_mro(self):
        @functools.singledispatch
        def g(obj):
            return "base"
        class A:
            pass
        class C(A):
            pass
        class B(A):
            pass
        class D(C, B):
            pass
        def g_A(a):
            return "A"
        def g_B(b):
            return "B"
        g.register(A, g_A)
        g.register(B, g_B)
        self.assertEqual(g(A()), "A")
        self.assertEqual(g(B()), "B")
        self.assertEqual(g(C()), "A")
        self.assertEqual(g(D()), "B")

    def test_register_decorator(self):
        @functools.singledispatch
        def g(obj):
            return "base"
        @g.register(int)
        def g_int(i):
            return "int %s" % (i,)
        self.assertEqual(g(""), "base")
        self.assertEqual(g(12), "int 12")
        self.assertIs(g.dispatch(int), g_int)
        self.assertIs(g.dispatch(object), g.dispatch(str))
        # Note: in the assert above this is not g.
        # @singledispatch returns the wrapper.

    def test_wrapping_attributes(self):
        @functools.singledispatch
        def g(obj):
            "Simple test"
            return "Test"
        self.assertEqual(g.__name__, "g")
        if sys.flags.optimize < 2:
            self.assertEqual(g.__doc__, "Simple test")

    @unittest.skipUnless(decimal, 'requires _decimal')
    @support.cpython_only
    def test_c_classes(self):
        @functools.singledispatch
        def g(obj):
            return "base"
        @g.register(decimal.DecimalException)
        def _(obj):
            return obj.args
        subn = decimal.Subnormal("Exponent < Emin")
        rnd = decimal.Rounded("Number got rounded")
        self.assertEqual(g(subn), ("Exponent < Emin",))
        self.assertEqual(g(rnd), ("Number got rounded",))
        @g.register(decimal.Subnormal)
        def _(obj):
            return "Too small to care."
        self.assertEqual(g(subn), "Too small to care.")
        self.assertEqual(g(rnd), ("Number got rounded",))

    def test_compose_mro(self):
        # None of the examples in this test depend on haystack ordering.
        c = collections.abc
        mro = functools._compose_mro
        bases = [c.Sequence, c.MutableMapping, c.Mapping, c.Set]
        for haystack in permutations(bases):
            m = mro(dict, haystack)
            self.assertEqual(m, [dict, c.MutableMapping, c.Mapping,
                                 c.Collection, c.Sized, c.Iterable,
                                 c.Container, object])
        bases = [c.Container, c.Mapping, c.MutableMapping, collections.OrderedDict]
        for haystack in permutations(bases):
            m = mro(collections.ChainMap, haystack)
            self.assertEqual(m, [collections.ChainMap, c.MutableMapping, c.Mapping,
                                 c.Collection, c.Sized, c.Iterable,
                                 c.Container, object])

        # If there's a generic function with implementations registered for
        # both Sized and Container, passing a defaultdict to it results in an
        # ambiguous dispatch which will cause a RuntimeError (see
        # test_mro_conflicts).
        bases = [c.Container, c.Sized, str]
        for haystack in permutations(bases):
            m = mro(collections.defaultdict, [c.Sized, c.Container, str])
            self.assertEqual(m, [collections.defaultdict, dict, c.Sized,
                                 c.Container, object])

        # MutableSequence below is registered directly on D. In other words, it
        # precedes MutableMapping which means single dispatch will always
        # choose MutableSequence here.
        class D(collections.defaultdict):
            pass
        c.MutableSequence.register(D)
        bases = [c.MutableSequence, c.MutableMapping]
        for haystack in permutations(bases):
            m = mro(D, bases)
            self.assertEqual(m, [D, c.MutableSequence, c.Sequence, c.Reversible,
                                 collections.defaultdict, dict, c.MutableMapping, c.Mapping,
                                 c.Collection, c.Sized, c.Iterable, c.Container,
                                 object])

        # Container and Callable are registered on different base classes and
        # a generic function supporting both should always pick the Callable
        # implementation if a C instance is passed.
        class C(collections.defaultdict):
            def __call__(self):
                pass
        bases = [c.Sized, c.Callable, c.Container, c.Mapping]
        for haystack in permutations(bases):
            m = mro(C, haystack)
            self.assertEqual(m, [C, c.Callable, collections.defaultdict, dict, c.Mapping,
                                 c.Collection, c.Sized, c.Iterable,
                                 c.Container, object])

    def test_register_abc(self):
        c = collections.abc
        d = {"a": "b"}
        l = [1, 2, 3]
        s = {object(), None}
        f = frozenset(s)
        t = (1, 2, 3)
        @functools.singledispatch
        def g(obj):
            return "base"
        self.assertEqual(g(d), "base")
        self.assertEqual(g(l), "base")
        self.assertEqual(g(s), "base")
        self.assertEqual(g(f), "base")
        self.assertEqual(g(t), "base")
        g.register(c.Sized, lambda obj: "sized")
        self.assertEqual(g(d), "sized")
        self.assertEqual(g(l), "sized")
        self.assertEqual(g(s), "sized")
        self.assertEqual(g(f), "sized")
        self.assertEqual(g(t), "sized")
        g.register(c.MutableMapping, lambda obj: "mutablemapping")
        self.assertEqual(g(d), "mutablemapping")
        self.assertEqual(g(l), "sized")
        self.assertEqual(g(s), "sized")
        self.assertEqual(g(f), "sized")
        self.assertEqual(g(t), "sized")
        g.register(collections.ChainMap, lambda obj: "chainmap")
        self.assertEqual(g(d), "mutablemapping")  # irrelevant ABCs registered
        self.assertEqual(g(l), "sized")
        self.assertEqual(g(s), "sized")
        self.assertEqual(g(f), "sized")
        self.assertEqual(g(t), "sized")
        g.register(c.MutableSequence, lambda obj: "mutablesequence")
        self.assertEqual(g(d), "mutablemapping")
        self.assertEqual(g(l), "mutablesequence")
        self.assertEqual(g(s), "sized")
        self.assertEqual(g(f), "sized")
        self.assertEqual(g(t), "sized")
        g.register(c.MutableSet, lambda obj: "mutableset")
        self.assertEqual(g(d), "mutablemapping")
        self.assertEqual(g(l), "mutablesequence")
        self.assertEqual(g(s), "mutableset")
        self.assertEqual(g(f), "sized")
        self.assertEqual(g(t), "sized")
        g.register(c.Mapping, lambda obj: "mapping")
        self.assertEqual(g(d), "mutablemapping")  # not specific enough
        self.assertEqual(g(l), "mutablesequence")
        self.assertEqual(g(s), "mutableset")
        self.assertEqual(g(f), "sized")
        self.assertEqual(g(t), "sized")
        g.register(c.Sequence, lambda obj: "sequence")
        self.assertEqual(g(d), "mutablemapping")
        self.assertEqual(g(l), "mutablesequence")
        self.assertEqual(g(s), "mutableset")
        self.assertEqual(g(f), "sized")
        self.assertEqual(g(t), "sequence")
        g.register(c.Set, lambda obj: "set")
        self.assertEqual(g(d), "mutablemapping")
        self.assertEqual(g(l), "mutablesequence")
        self.assertEqual(g(s), "mutableset")
        self.assertEqual(g(f), "set")
        self.assertEqual(g(t), "sequence")
        g.register(dict, lambda obj: "dict")
        self.assertEqual(g(d), "dict")
        self.assertEqual(g(l), "mutablesequence")
        self.assertEqual(g(s), "mutableset")
        self.assertEqual(g(f), "set")
        self.assertEqual(g(t), "sequence")
        g.register(list, lambda obj: "list")
        self.assertEqual(g(d), "dict")
        self.assertEqual(g(l), "list")
        self.assertEqual(g(s), "mutableset")
        self.assertEqual(g(f), "set")
        self.assertEqual(g(t), "sequence")
        g.register(set, lambda obj: "concrete-set")
        self.assertEqual(g(d), "dict")
        self.assertEqual(g(l), "list")
        self.assertEqual(g(s), "concrete-set")
        self.assertEqual(g(f), "set")
        self.assertEqual(g(t), "sequence")
        g.register(frozenset, lambda obj: "frozen-set")
        self.assertEqual(g(d), "dict")
        self.assertEqual(g(l), "list")
        self.assertEqual(g(s), "concrete-set")
        self.assertEqual(g(f), "frozen-set")
        self.assertEqual(g(t), "sequence")
        g.register(tuple, lambda obj: "tuple")
        self.assertEqual(g(d), "dict")
        self.assertEqual(g(l), "list")
        self.assertEqual(g(s), "concrete-set")
        self.assertEqual(g(f), "frozen-set")
        self.assertEqual(g(t), "tuple")

    def test_c3_abc(self):
        c = collections.abc
        mro = functools._c3_mro
        class A(object):
            pass
        class B(A):
            def __len__(self):
                return 0   # implies Sized
        @c.Container.register
        class C(object):
            pass
        class D(object):
            pass   # unrelated
        class X(D, C, B):
            def __call__(self):
                pass   # implies Callable
        expected = [X, c.Callable, D, C, c.Container, B, c.Sized, A, object]
        for abcs in permutations([c.Sized, c.Callable, c.Container]):
            self.assertEqual(mro(X, abcs=abcs), expected)
        # unrelated ABCs don't appear in the resulting MRO
        many_abcs = [c.Mapping, c.Sized, c.Callable, c.Container, c.Iterable]
        self.assertEqual(mro(X, abcs=many_abcs), expected)

    def test_false_meta(self):
        # see issue23572
        class MetaA(type):
            def __len__(self):
                return 0
        class A(metaclass=MetaA):
            pass
        class AA(A):
            pass
        @functools.singledispatch
        def fun(a):
            return 'base A'
        @fun.register(A)
        def _(a):
            return 'fun A'
        aa = AA()
        self.assertEqual(fun(aa), 'fun A')

    def test_mro_conflicts(self):
        c = collections.abc
        @functools.singledispatch
        def g(arg):
            return "base"
        class O(c.Sized):
            def __len__(self):
                return 0
        o = O()
        self.assertEqual(g(o), "base")
        g.register(c.Iterable, lambda arg: "iterable")
        g.register(c.Container, lambda arg: "container")
        g.register(c.Sized, lambda arg: "sized")
        g.register(c.Set, lambda arg: "set")
        self.assertEqual(g(o), "sized")
        c.Iterable.register(O)
        self.assertEqual(g(o), "sized")   # because it's explicitly in __mro__
        c.Container.register(O)
        self.assertEqual(g(o), "sized")   # see above: Sized is in __mro__
        c.Set.register(O)
        self.assertEqual(g(o), "set")     # because c.Set is a subclass of
                                          # c.Sized and c.Container
        class P:
            pass
        p = P()
        self.assertEqual(g(p), "base")
        c.Iterable.register(P)
        self.assertEqual(g(p), "iterable")
        c.Container.register(P)
        with self.assertRaises(RuntimeError) as re_one:
            g(p)
        self.assertIn(
            str(re_one.exception),
            (("Ambiguous dispatch: <class 'collections.abc.Container'> "
              "or <class 'collections.abc.Iterable'>"),
             ("Ambiguous dispatch: <class 'collections.abc.Iterable'> "
              "or <class 'collections.abc.Container'>")),
        )
        class Q(c.Sized):
            def __len__(self):
                return 0
        q = Q()
        self.assertEqual(g(q), "sized")
        c.Iterable.register(Q)
        self.assertEqual(g(q), "sized")   # because it's explicitly in __mro__
        c.Set.register(Q)
        self.assertEqual(g(q), "set")     # because c.Set is a subclass of
                                          # c.Sized and c.Iterable
        @functools.singledispatch
        def h(arg):
            return "base"
        @h.register(c.Sized)
        def _(arg):
            return "sized"
        @h.register(c.Container)
        def _(arg):
            return "container"
        # Even though Sized and Container are explicit bases of MutableMapping,
        # this ABC is implicitly registered on defaultdict which makes all of
        # MutableMapping's bases implicit as well from defaultdict's
        # perspective.
        with self.assertRaises(RuntimeError) as re_two:
            h(collections.defaultdict(lambda: 0))
        self.assertIn(
            str(re_two.exception),
            (("Ambiguous dispatch: <class 'collections.abc.Container'> "
              "or <class 'collections.abc.Sized'>"),
             ("Ambiguous dispatch: <class 'collections.abc.Sized'> "
              "or <class 'collections.abc.Container'>")),
        )
        class R(collections.defaultdict):
            pass
        c.MutableSequence.register(R)
        @functools.singledispatch
        def i(arg):
            return "base"
        @i.register(c.MutableMapping)
        def _(arg):
            return "mapping"
        @i.register(c.MutableSequence)
        def _(arg):
            return "sequence"
        r = R()
        self.assertEqual(i(r), "sequence")
        class S:
            pass
        class T(S, c.Sized):
            def __len__(self):
                return 0
        t = T()
        self.assertEqual(h(t), "sized")
        c.Container.register(T)
        self.assertEqual(h(t), "sized")   # because it's explicitly in the MRO
        class U:
            def __len__(self):
                return 0
        u = U()
        self.assertEqual(h(u), "sized")   # implicit Sized subclass inferred
                                          # from the existence of __len__()
        c.Container.register(U)
        # There is no preference for registered versus inferred ABCs.
        with self.assertRaises(RuntimeError) as re_three:
            h(u)
        self.assertIn(
            str(re_three.exception),
            (("Ambiguous dispatch: <class 'collections.abc.Container'> "
              "or <class 'collections.abc.Sized'>"),
             ("Ambiguous dispatch: <class 'collections.abc.Sized'> "
              "or <class 'collections.abc.Container'>")),
        )
        class V(c.Sized, S):
            def __len__(self):
                return 0
        @functools.singledispatch
        def j(arg):
            return "base"
        @j.register(S)
        def _(arg):
            return "s"
        @j.register(c.Container)
        def _(arg):
            return "container"
        v = V()
        self.assertEqual(j(v), "s")
        c.Container.register(V)
        self.assertEqual(j(v), "container")   # because it ends up right after
                                              # Sized in the MRO

    def test_cache_invalidation(self):
        from collections import UserDict
        import weakref

        class TracingDict(UserDict):
            def __init__(self, *args, **kwargs):
                super(TracingDict, self).__init__(*args, **kwargs)
                self.set_ops = []
                self.get_ops = []
            def __getitem__(self, key):
                result = self.data[key]
                self.get_ops.append(key)
                return result
            def __setitem__(self, key, value):
                self.set_ops.append(key)
                self.data[key] = value
            def clear(self):
                self.data.clear()

        td = TracingDict()
        with support.swap_attr(weakref, "WeakKeyDictionary", lambda: td):
            c = collections.abc
            @functools.singledispatch
            def g(arg):
                return "base"
            d = {}
            l = []
            self.assertEqual(len(td), 0)
            self.assertEqual(g(d), "base")
            self.assertEqual(len(td), 1)
            self.assertEqual(td.get_ops, [])
            self.assertEqual(td.set_ops, [dict])
            self.assertEqual(td.data[dict], g.registry[object])
            self.assertEqual(g(l), "base")
            self.assertEqual(len(td), 2)
            self.assertEqual(td.get_ops, [])
            self.assertEqual(td.set_ops, [dict, list])
            self.assertEqual(td.data[dict], g.registry[object])
            self.assertEqual(td.data[list], g.registry[object])
            self.assertEqual(td.data[dict], td.data[list])
            self.assertEqual(g(l), "base")
            self.assertEqual(g(d), "base")
            self.assertEqual(td.get_ops, [list, dict])
            self.assertEqual(td.set_ops, [dict, list])
            g.register(list, lambda arg: "list")
            self.assertEqual(td.get_ops, [list, dict])
            self.assertEqual(len(td), 0)
            self.assertEqual(g(d), "base")
            self.assertEqual(len(td), 1)
            self.assertEqual(td.get_ops, [list, dict])
            self.assertEqual(td.set_ops, [dict, list, dict])
            self.assertEqual(td.data[dict],
                             functools._find_impl(dict, g.registry))
            self.assertEqual(g(l), "list")
            self.assertEqual(len(td), 2)
            self.assertEqual(td.get_ops, [list, dict])
            self.assertEqual(td.set_ops, [dict, list, dict, list])
            self.assertEqual(td.data[list],
                             functools._find_impl(list, g.registry))
            class X:
                pass
            c.MutableMapping.register(X)   # Will not invalidate the cache,
                                           # not using ABCs yet.
            self.assertEqual(g(d), "base")
            self.assertEqual(g(l), "list")
            self.assertEqual(td.get_ops, [list, dict, dict, list])
            self.assertEqual(td.set_ops, [dict, list, dict, list])
            g.register(c.Sized, lambda arg: "sized")
            self.assertEqual(len(td), 0)
            self.assertEqual(g(d), "sized")
            self.assertEqual(len(td), 1)
            self.assertEqual(td.get_ops, [list, dict, dict, list])
            self.assertEqual(td.set_ops, [dict, list, dict, list, dict])
            self.assertEqual(g(l), "list")
            self.assertEqual(len(td), 2)
            self.assertEqual(td.get_ops, [list, dict, dict, list])
            self.assertEqual(td.set_ops, [dict, list, dict, list, dict, list])
            self.assertEqual(g(l), "list")
            self.assertEqual(g(d), "sized")
            self.assertEqual(td.get_ops, [list, dict, dict, list, list, dict])
            self.assertEqual(td.set_ops, [dict, list, dict, list, dict, list])
            g.dispatch(list)
            g.dispatch(dict)
            self.assertEqual(td.get_ops, [list, dict, dict, list, list, dict,
                                          list, dict])
            self.assertEqual(td.set_ops, [dict, list, dict, list, dict, list])
            c.MutableSet.register(X)       # Will invalidate the cache.
            self.assertEqual(len(td), 2)   # Stale cache.
            self.assertEqual(g(l), "list")
            self.assertEqual(len(td), 1)
            g.register(c.MutableMapping, lambda arg: "mutablemapping")
            self.assertEqual(len(td), 0)
            self.assertEqual(g(d), "mutablemapping")
            self.assertEqual(len(td), 1)
            self.assertEqual(g(l), "list")
            self.assertEqual(len(td), 2)
            g.register(dict, lambda arg: "dict")
            self.assertEqual(g(d), "dict")
            self.assertEqual(g(l), "list")
            g._clear_cache()
            self.assertEqual(len(td), 0)

    def test_annotations(self):
        @functools.singledispatch
        def i(arg):
            return "base"
        @i.register
        def _(arg: collections.abc.Mapping):
            return "mapping"
        @i.register
        def _(arg: "collections.abc.Sequence"):
            return "sequence"
        self.assertEqual(i(None), "base")
        self.assertEqual(i({"a": 1}), "mapping")
        self.assertEqual(i([1, 2, 3]), "sequence")
        self.assertEqual(i((1, 2, 3)), "sequence")
        self.assertEqual(i("str"), "sequence")

        # Registering classes as callables doesn't work with annotations,
        # you need to pass the type explicitly.
        @i.register(str)
        class _:
            def __init__(self, arg):
                self.arg = arg

            def __eq__(self, other):
                return self.arg == other
        self.assertEqual(i("str"), "str")

    def test_invalid_registrations(self):
        msg_prefix = "Invalid first argument to `register()`: "
        msg_suffix = (
            ". Use either `@register(some_class)` or plain `@register` on an "
            "annotated function."
        )
        @functools.singledispatch
        def i(arg):
            return "base"
        with self.assertRaises(TypeError) as exc:
            @i.register(42)
            def _(arg):
                return "I annotated with a non-type"
        self.assertTrue(str(exc.exception).startswith(msg_prefix + "42"))
        self.assertTrue(str(exc.exception).endswith(msg_suffix))
        with self.assertRaises(TypeError) as exc:
            @i.register
            def _(arg):
                return "I forgot to annotate"
        self.assertTrue(str(exc.exception).startswith(msg_prefix +
            "<function TestSingleDispatch.test_invalid_registrations.<locals>._"
        ))
        self.assertTrue(str(exc.exception).endswith(msg_suffix))

        # FIXME: The following will only work after PEP 560 is implemented.
        return

        with self.assertRaises(TypeError) as exc:
            @i.register
            def _(arg: typing.Iterable[str]):
                # At runtime, dispatching on generics is impossible.
                # When registering implementations with singledispatch, avoid
                # types from `typing`. Instead, annotate with regular types
                # or ABCs.
                return "I annotated with a generic collection"
        self.assertTrue(str(exc.exception).startswith(msg_prefix +
            "<function TestSingleDispatch.test_invalid_registrations.<locals>._"
        ))
        self.assertTrue(str(exc.exception).endswith(msg_suffix))

    def test_invalid_positional_argument(self):
        @functools.singledispatch
        def f(*args):
            pass
        msg = 'f requires at least 1 positional argument'
        with self.assertRaisesRegex(TypeError, msg):
            f()

if __name__ == '__main__':
    unittest.main()