helper to check picklability tests an implementation detail where tuple is reused whenever nothing else holds a reference to it bpo42536 enumerate s tuplereuse speed trick breaks the gc s assumptions about what can be untracked make sure we retrack result tuples whenever we reuse them that gc collection probably untracked the recycled internal result tuple which is initialized to none none make sure it s retracked when it s mutated and returned from next don t allow keyword arguments this bug was never in reversed it was in pyobjectcallmethod and reversednew calls that sometimes objects must have len and getitem implemented helper to check picklability no arguments wrong type not iterable wrong type too many arguments tests an implementation detail where tuple is reused whenever nothing else holds a reference to it bpo 42536 enumerate s tuple reuse speed trick breaks the gc s assumptions about what can be untracked make sure we re track result tuples whenever we reuse them that gc collection probably untracked the recycled internal result tuple which is initialized to none none make sure it s re tracked when it s mutated and returned from __next__ don t allow keyword arguments this bug was never in reversed it was in pyobject_callmethod and reversed_new calls that sometimes objects must have __len__ and __getitem__ implemented
import unittest
import operator
import sys
import pickle
import gc

from test import support

class G:
    'Sequence using __getitem__'
    def __init__(self, seqn):
        self.seqn = seqn
    def __getitem__(self, i):
        return self.seqn[i]

class I:
    'Sequence using iterator protocol'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __iter__(self):
        return self
    def __next__(self):
        if self.i >= len(self.seqn): raise StopIteration
        v = self.seqn[self.i]
        self.i += 1
        return v

class Ig:
    'Sequence using iterator protocol defined with a generator'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __iter__(self):
        for val in self.seqn:
            yield val

class X:
    'Missing __getitem__ and __iter__'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __next__(self):
        if self.i >= len(self.seqn): raise StopIteration
        v = self.seqn[self.i]
        self.i += 1
        return v

class E:
    'Test propagation of exceptions'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __iter__(self):
        return self
    def __next__(self):
        3 // 0

class N:
    'Iterator missing __next__()'
    def __init__(self, seqn):
        self.seqn = seqn
        self.i = 0
    def __iter__(self):
        return self

class PickleTest:
    
    def check_pickle(self, itorg, seq):
        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
            d = pickle.dumps(itorg, proto)
            it = pickle.loads(d)
            self.assertEqual(type(itorg), type(it))
            self.assertEqual(list(it), seq)

            it = pickle.loads(d)
            try:
                next(it)
            except StopIteration:
                self.assertFalse(seq[1:])
                continue
            d = pickle.dumps(it, proto)
            it = pickle.loads(d)
            self.assertEqual(list(it), seq[1:])

class EnumerateTestCase(unittest.TestCase, PickleTest):

    enum = enumerate
    seq, res = 'abc', [(0,'a'), (1,'b'), (2,'c')]

    def test_basicfunction(self):
        self.assertEqual(type(self.enum(self.seq)), self.enum)
        e = self.enum(self.seq)
        self.assertEqual(iter(e), e)
        self.assertEqual(list(self.enum(self.seq)), self.res)
        self.enum.__doc__

    def test_pickle(self):
        self.check_pickle(self.enum(self.seq), self.res)

    def test_getitemseqn(self):
        self.assertEqual(list(self.enum(G(self.seq))), self.res)
        e = self.enum(G(''))
        self.assertRaises(StopIteration, next, e)

    def test_iteratorseqn(self):
        self.assertEqual(list(self.enum(I(self.seq))), self.res)
        e = self.enum(I(''))
        self.assertRaises(StopIteration, next, e)

    def test_iteratorgenerator(self):
        self.assertEqual(list(self.enum(Ig(self.seq))), self.res)
        e = self.enum(Ig(''))
        self.assertRaises(StopIteration, next, e)

    def test_noniterable(self):
        self.assertRaises(TypeError, self.enum, X(self.seq))

    def test_illformediterable(self):
        self.assertRaises(TypeError, self.enum, N(self.seq))

    def test_exception_propagation(self):
        self.assertRaises(ZeroDivisionError, list, self.enum(E(self.seq)))

    def test_argumentcheck(self):
        self.assertRaises(TypeError, self.enum) 
        self.assertRaises(TypeError, self.enum, 1) 
        self.assertRaises(TypeError, self.enum, 'abc', 'a') 
        self.assertRaises(TypeError, self.enum, 'abc', 2, 3) 

    def test_kwargs(self):
        self.assertEqual(list(self.enum(iterable=Ig(self.seq))), self.res)
        expected = list(self.enum(Ig(self.seq), 0))
        self.assertEqual(list(self.enum(iterable=Ig(self.seq), start=0)),
                         expected)
        self.assertEqual(list(self.enum(start=0, iterable=Ig(self.seq))),
                         expected)
        self.assertRaises(TypeError, self.enum, iterable=[], x=3)
        self.assertRaises(TypeError, self.enum, start=0, x=3)
        self.assertRaises(TypeError, self.enum, x=0, y=3)
        self.assertRaises(TypeError, self.enum, x=0)

    @support.cpython_only
    def test_tuple_reuse(self):
        
        
        self.assertEqual(len(set(map(id, list(enumerate(self.seq))))), len(self.seq))
        self.assertEqual(len(set(map(id, enumerate(self.seq)))), min(1,len(self.seq)))

    @support.cpython_only
    def test_enumerate_result_gc(self):
        
        
        
        it = self.enum([[]])
        gc.collect()
        
        
        
        self.assertTrue(gc.is_tracked(next(it)))

class MyEnum(enumerate):
    pass

class SubclassTestCase(EnumerateTestCase):

    enum = MyEnum

class TestEmpty(EnumerateTestCase):

    seq, res = '', []

class TestBig(EnumerateTestCase):

    seq = range(10,20000,2)
    res = list(zip(range(20000), seq))

class TestReversed(unittest.TestCase, PickleTest):

    def test_simple(self):
        class A:
            def __getitem__(self, i):
                if i < 5:
                    return str(i)
                raise StopIteration
            def __len__(self):
                return 5
        for data in ('abc', range(5), tuple(enumerate('abc')), A(),
                    range(1,17,5), dict.fromkeys('abcde')):
            self.assertEqual(list(data)[::-1], list(reversed(data)))
        
        self.assertRaises(TypeError, reversed, [], a=1)

    def test_range_optimization(self):
        x = range(1)
        self.assertEqual(type(reversed(x)), type(iter(x)))

    def test_len(self):
        for s in ('hello', tuple('hello'), list('hello'), range(5)):
            self.assertEqual(operator.length_hint(reversed(s)), len(s))
            r = reversed(s)
            list(r)
            self.assertEqual(operator.length_hint(r), 0)
        class SeqWithWeirdLen:
            called = False
            def __len__(self):
                if not self.called:
                    self.called = True
                    return 10
                raise ZeroDivisionError
            def __getitem__(self, index):
                return index
        r = reversed(SeqWithWeirdLen())
        self.assertRaises(ZeroDivisionError, operator.length_hint, r)


    def test_gc(self):
        class Seq:
            def __len__(self):
                return 10
            def __getitem__(self, index):
                return index
        s = Seq()
        r = reversed(s)
        s.r = r

    def test_args(self):
        self.assertRaises(TypeError, reversed)
        self.assertRaises(TypeError, reversed, [], 'extra')

    @unittest.skipUnless(hasattr(sys, 'getrefcount'), 'test needs sys.getrefcount()')
    def test_bug1229429(self):
        
        
        def f():
            pass
        r = f.__reversed__ = object()
        rc = sys.getrefcount(r)
        for i in range(10):
            try:
                reversed(f)
            except TypeError:
                pass
            else:
                self.fail("non-callable __reversed__ didn't raise!")
        self.assertEqual(rc, sys.getrefcount(r))

    def test_objmethods(self):
        
        class NoLen(object):
            def __getitem__(self, i): return 1
        nl = NoLen()
        self.assertRaises(TypeError, reversed, nl)

        class NoGetItem(object):
            def __len__(self): return 2
        ngi = NoGetItem()
        self.assertRaises(TypeError, reversed, ngi)

        class Blocked(object):
            def __getitem__(self, i): return 1
            def __len__(self): return 2
            __reversed__ = None
        b = Blocked()
        self.assertRaises(TypeError, reversed, b)

    def test_pickle(self):
        for data in 'abc', range(5), tuple(enumerate('abc')), range(1,17,5):
            self.check_pickle(reversed(data), list(data)[::-1])


class EnumerateStartTestCase(EnumerateTestCase):

    def test_basicfunction(self):
        e = self.enum(self.seq)
        self.assertEqual(iter(e), e)
        self.assertEqual(list(self.enum(self.seq)), self.res)


class TestStart(EnumerateStartTestCase):
    def enum(self, iterable, start=11):
        return enumerate(iterable, start=start)

    seq, res = 'abc', [(11, 'a'), (12, 'b'), (13, 'c')]


class TestLongStart(EnumerateStartTestCase):
    def enum(self, iterable, start=sys.maxsize + 1):
        return enumerate(iterable, start=start)

    seq, res = 'abc', [(sys.maxsize+1,'a'), (sys.maxsize+2,'b'),
                       (sys.maxsize+3,'c')]


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