Python collections.Counter.update() Examples

def test_inplace_operations(self):
        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for inplace_op, regular_op in [
                (Counter.__iadd__, Counter.__add__),
                (Counter.__isub__, Counter.__sub__),
                (Counter.__ior__, Counter.__or__),
                (Counter.__iand__, Counter.__and__),
            ]:
                c = p.copy()
                c_id = id(c)
                regular_result = regular_op(c, q)
                inplace_result = inplace_op(c, q)
                self.assertEqual(inplace_result, regular_result)
                self.assertEqual(id(inplace_result), c_id) 

def test_copying(self):
        # Check that counters are copyable, deepcopyable, picklable, and
        #have a repr/eval round-trip
        words = Counter('which witch had which witches wrist watch'.split())
        def check(dup):
            msg = "\ncopy: %s\nwords: %s" % (dup, words)
            self.assertIsNot(dup, words, msg)
            self.assertEqual(dup, words)
        check(words.copy())
        check(copy.copy(words))
        check(copy.deepcopy(words))
        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
            with self.subTest(proto=proto):
                check(pickle.loads(pickle.dumps(words, proto)))
        check(eval(repr(words)))
        update_test = Counter()
        update_test.update(words)
        check(update_test)
        check(Counter(words)) 

def test_inplace_operations(self):
        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for inplace_op, regular_op in [
                (Counter.__iadd__, Counter.__add__),
                (Counter.__isub__, Counter.__sub__),
                (Counter.__ior__, Counter.__or__),
                (Counter.__iand__, Counter.__and__),
            ]:
                c = p.copy()
                c_id = id(c)
                regular_result = regular_op(c, q)
                inplace_result = inplace_op(c, q)
                self.assertEqual(inplace_result, regular_result)
                self.assertEqual(id(inplace_result), c_id) 

def test_copying(self):
        # Check that counters are copyable, deepcopyable, picklable, and
        #have a repr/eval round-trip
        words = Counter('which witch had which witches wrist watch'.split())
        def check(dup):
            msg = "\ncopy: %s\nwords: %s" % (dup, words)
            self.assertIsNot(dup, words, msg)
            self.assertEqual(dup, words)
        check(words.copy())
        check(copy.copy(words))
        check(copy.deepcopy(words))
        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
            with self.subTest(proto=proto):
                check(pickle.loads(pickle.dumps(words, proto)))
        check(eval(repr(words)))
        update_test = Counter()
        update_test.update(words)
        check(update_test)
        check(Counter(words)) 

def test_inplace_operations(self):
        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for inplace_op, regular_op in [
                (Counter.__iadd__, Counter.__add__),
                (Counter.__isub__, Counter.__sub__),
                (Counter.__ior__, Counter.__or__),
                (Counter.__iand__, Counter.__and__),
            ]:
                c = p.copy()
                c_id = id(c)
                regular_result = regular_op(c, q)
                inplace_result = inplace_op(c, q)
                self.assertEqual(inplace_result, regular_result)
                self.assertEqual(id(inplace_result), c_id) 

def test_copying(self):
        # Check that counters are copyable, deepcopyable, picklable, and
        #have a repr/eval round-trip
        words = Counter('which witch had which witches wrist watch'.split())
        def check(dup):
            msg = "\ncopy: %s\nwords: %s" % (dup, words)
            self.assertIsNot(dup, words, msg)
            self.assertEqual(dup, words)
        check(words.copy())
        check(copy.copy(words))
        check(copy.deepcopy(words))
        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
            with self.subTest(proto=proto):
                check(pickle.loads(pickle.dumps(words, proto)))
        check(eval(repr(words)))
        update_test = Counter()
        update_test.update(words)
        check(update_test)
        check(Counter(words)) 

def __init__(self, samples=None):
        """
        Construct a new frequency distribution.  If ``samples`` is
        given, then the frequency distribution will be initialized
        with the count of each object in ``samples``; otherwise, it
        will be initialized to be empty.

        In particular, ``FreqDist()`` returns an empty frequency
        distribution; and ``FreqDist(samples)`` first creates an empty
        frequency distribution, and then calls ``update`` with the
        list ``samples``.

        :param samples: The samples to initialize the frequency
            distribution with.
        :type samples: Sequence
        """
        Counter.__init__(self, samples)

        # Cached number of samples in this FreqDist
        self._N = None 

def test_copying(self):
        # Check that ordered dicts are copyable, deepcopyable, picklable,
        # and have a repr/eval round-trip
        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
        od = OrderedDict(pairs)
        update_test = OrderedDict()
        update_test.update(od)
        for i, dup in enumerate([
                    od.copy(),
                    copy.copy(od),
                    copy.deepcopy(od),
                    pickle.loads(pickle.dumps(od, 0)),
                    pickle.loads(pickle.dumps(od, 1)),
                    pickle.loads(pickle.dumps(od, 2)),
                    pickle.loads(pickle.dumps(od, -1)),
                    eval(repr(od)),
                    update_test,
                    OrderedDict(od),
                    ]):
            self.assertTrue(dup is not od)
            self.assertEqual(dup, od)
            self.assertEqual(list(dup.items()), list(od.items()))
            self.assertEqual(len(dup), len(od))
            self.assertEqual(type(dup), type(od)) 

def test_copying(self):
        # Check that counters are copyable, deepcopyable, picklable, and
        #have a repr/eval round-trip
        words = Counter('which witch had which witches wrist watch'.split())
        def check(dup):
            msg = "\ncopy: %s\nwords: %s" % (dup, words)
            self.assertIsNot(dup, words, msg)
            self.assertEqual(dup, words)
        check(words.copy())
        check(copy.copy(words))
        check(copy.deepcopy(words))
        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
            with self.subTest(proto=proto):
                check(pickle.loads(pickle.dumps(words, proto)))
        check(eval(repr(words)))
        update_test = Counter()
        update_test.update(words)
        check(update_test)
        check(Counter(words)) 

def update(self, *args, **kwargs):
        """
        Override ``Counter.update()`` to invalidate the cached N
        """
        self._N = None
        super(FreqDist, self).update(*args, **kwargs) 

def test_update(self):
        c = Counter()
        c.update(self=42)
        self.assertEqual(list(c.items()), [('self', 42)])
        c = Counter()
        c.update(iterable=42)
        self.assertEqual(list(c.items()), [('iterable', 42)])
        c = Counter()
        c.update(iterable=None)
        self.assertEqual(list(c.items()), [('iterable', None)])
        self.assertRaises(TypeError, Counter().update, 42)
        self.assertRaises(TypeError, Counter().update, {}, {})
        self.assertRaises(TypeError, Counter.update) 

def __init__(self, probdist_dict):
        """
        :param probdist_dict: a dictionary containing the probdists indexed
            by the conditions
        :type probdist_dict: dict any -> probdist
        """
        self.update(probdist_dict) 

def test_multiset_operations(self):
        # Verify that adding a zero counter will strip zeros and negatives
        c = Counter(a=10, b=-2, c=0) + Counter()
        self.assertEqual(dict(c), dict(a=10))

        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for counterop, numberop in [
                (Counter.__add__, lambda x, y: max(0, x+y)),
                (Counter.__sub__, lambda x, y: max(0, x-y)),
                (Counter.__or__, lambda x, y: max(0,x,y)),
                (Counter.__and__, lambda x, y: max(0, min(x,y))),
            ]:
                result = counterop(p, q)
                for x in elements:
                    self.assertEqual(numberop(p[x], q[x]), result[x],
                                     (counterop, x, p, q))
                # verify that results exclude non-positive counts
                self.assertTrue(x>0 for x in result.values())

        elements = 'abcdef'
        for i in range(100):
            # verify that random multisets with no repeats are exactly like sets
            p = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            q = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            for counterop, setop in [
                (Counter.__sub__, set.__sub__),
                (Counter.__or__, set.__or__),
                (Counter.__and__, set.__and__),
            ]:
                counter_result = counterop(p, q)
                set_result = setop(set(p.elements()), set(q.elements()))
                self.assertEqual(counter_result, dict.fromkeys(set_result, 1)) 

def test_ordering(self):
        # Combined order matches a series of dict updates from last to first.
        # This test relies on the ordering of the underlying dicts.

        baseline = {'music': 'bach', 'art': 'rembrandt'}
        adjustments = {'art': 'van gogh', 'opera': 'carmen'}

        cm = ChainMap(adjustments, baseline)

        combined = baseline.copy()
        combined.update(adjustments)

        self.assertEqual(list(combined.items()), list(cm.items())) 

def test_update(self):
        c = Counter()
        c.update(self=42)
        self.assertEqual(list(c.items()), [('self', 42)])
        c = Counter()
        c.update(iterable=42)
        self.assertEqual(list(c.items()), [('iterable', 42)])
        c = Counter()
        c.update(iterable=None)
        self.assertEqual(list(c.items()), [('iterable', None)])
        self.assertRaises(TypeError, Counter().update, 42)
        self.assertRaises(TypeError, Counter().update, {}, {})
        self.assertRaises(TypeError, Counter.update) 

def test_update(self):
        c = Counter()
        c.update(self=42)
        self.assertEqual(list(c.items()), [('self', 42)])
        c = Counter()
        c.update(iterable=42)
        self.assertEqual(list(c.items()), [('iterable', 42)])
        c = Counter()
        c.update(iterable=None)
        self.assertEqual(list(c.items()), [('iterable', None)])
        self.assertRaises(TypeError, Counter().update, 42)
        self.assertRaises(TypeError, Counter().update, {}, {})
        self.assertRaises(TypeError, Counter.update) 

def test_multiset_operations(self):
        # Verify that adding a zero counter will strip zeros and negatives
        c = Counter(a=10, b=-2, c=0) + Counter()
        self.assertEqual(dict(c), dict(a=10))

        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for counterop, numberop in [
                (Counter.__add__, lambda x, y: max(0, x+y)),
                (Counter.__sub__, lambda x, y: max(0, x-y)),
                (Counter.__or__, lambda x, y: max(0,x,y)),
                (Counter.__and__, lambda x, y: max(0, min(x,y))),
            ]:
                result = counterop(p, q)
                for x in elements:
                    self.assertEqual(numberop(p[x], q[x]), result[x],
                                     (counterop, x, p, q))
                # verify that results exclude non-positive counts
                self.assertTrue(x>0 for x in result.values())

        elements = 'abcdef'
        for i in range(100):
            # verify that random multisets with no repeats are exactly like sets
            p = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            q = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            for counterop, setop in [
                (Counter.__sub__, set.__sub__),
                (Counter.__or__, set.__or__),
                (Counter.__and__, set.__and__),
            ]:
                counter_result = counterop(p, q)
                set_result = setop(set(p.elements()), set(q.elements()))
                self.assertEqual(counter_result, dict.fromkeys(set_result, 1)) 

def test_multiset_operations(self):
        # Verify that adding a zero counter will strip zeros and negatives
        c = Counter(a=10, b=-2, c=0) + Counter()
        self.assertEqual(dict(c), dict(a=10))

        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for counterop, numberop in [
                (Counter.__add__, lambda x, y: max(0, x+y)),
                (Counter.__sub__, lambda x, y: max(0, x-y)),
                (Counter.__or__, lambda x, y: max(0,x,y)),
                (Counter.__and__, lambda x, y: max(0, min(x,y))),
            ]:
                result = counterop(p, q)
                for x in elements:
                    self.assertEqual(numberop(p[x], q[x]), result[x],
                                     (counterop, x, p, q))
                # verify that results exclude non-positive counts
                self.assertTrue(x>0 for x in result.values())

        elements = 'abcdef'
        for i in range(100):
            # verify that random multisets with no repeats are exactly like sets
            p = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            q = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            for counterop, setop in [
                (Counter.__sub__, set.__sub__),
                (Counter.__or__, set.__or__),
                (Counter.__and__, set.__and__),
            ]:
                counter_result = counterop(p, q)
                set_result = setop(set(p.elements()), set(q.elements()))
                self.assertEqual(counter_result, dict.fromkeys(set_result, 1)) 

def test_copying(self):
        # Check that counters are copyable, deepcopyable, picklable, and
        #have a repr/eval round-trip
        words = Counter('which witch had which witches wrist watch'.split())
        update_test = Counter()
        update_test.update(words)
        for i, dup in enumerate([
                    words.copy(),
                    copy.copy(words),
                    copy.deepcopy(words),
                    pickle.loads(pickle.dumps(words, 0)),
                    pickle.loads(pickle.dumps(words, 1)),
                    pickle.loads(pickle.dumps(words, 2)),
                    pickle.loads(pickle.dumps(words, -1)),
                    cPickle.loads(cPickle.dumps(words, 0)),
                    cPickle.loads(cPickle.dumps(words, 1)),
                    cPickle.loads(cPickle.dumps(words, 2)),
                    cPickle.loads(cPickle.dumps(words, -1)),
                    eval(repr(words)),
                    update_test,
                    Counter(words),
                    ]):
            msg = (i, dup, words)
            self.assertTrue(dup is not words)
            self.assertEqual(dup, words)
            self.assertEqual(len(dup), len(words))
            self.assertEqual(type(dup), type(words)) 

def test_dict_update(self):
        od = OrderedDict()
        dict.update(od, [('spam', 1)])
        self.assertNotIn('NULL', repr(od)) 

def test_multiset_operations(self):
        # Verify that adding a zero counter will strip zeros and negatives
        c = Counter(a=10, b=-2, c=0) + Counter()
        self.assertEqual(dict(c), dict(a=10))

        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for counterop, numberop in [
                (Counter.__add__, lambda x, y: max(0, x+y)),
                (Counter.__sub__, lambda x, y: max(0, x-y)),
                (Counter.__or__, lambda x, y: max(0,x,y)),
                (Counter.__and__, lambda x, y: max(0, min(x,y))),
            ]:
                result = counterop(p, q)
                for x in elements:
                    self.assertEqual(numberop(p[x], q[x]), result[x],
                                     (counterop, x, p, q))
                # verify that results exclude non-positive counts
                self.assertTrue(x>0 for x in result.values())

        elements = 'abcdef'
        for i in range(100):
            # verify that random multisets with no repeats are exactly like sets
            p = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            q = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            for counterop, setop in [
                (Counter.__sub__, set.__sub__),
                (Counter.__or__, set.__or__),
                (Counter.__and__, set.__and__),
            ]:
                counter_result = counterop(p, q)
                set_result = setop(set(p.elements()), set(q.elements()))
                self.assertEqual(counter_result, dict.fromkeys(set_result, 1)) 

def test_override_update(self):
        OrderedDict = self.OrderedDict
        # Verify that subclasses can override update() without breaking __init__()
        class MyOD(OrderedDict):
            def update(self, *args, **kwds):
                raise Exception()
        items = [('a', 1), ('c', 3), ('b', 2)]
        self.assertEqual(list(MyOD(items).items()), items) 

def test_copying(self):
        OrderedDict = self.OrderedDict
        # Check that ordered dicts are copyable, deepcopyable, picklable,
        # and have a repr/eval round-trip
        pairs = [('c', 1), ('b', 2), ('a', 3), ('d', 4), ('e', 5), ('f', 6)]
        od = OrderedDict(pairs)
        def check(dup):
            msg = "\ncopy: %s\nod: %s" % (dup, od)
            self.assertIsNot(dup, od, msg)
            self.assertEqual(dup, od)
            self.assertEqual(list(dup.items()), list(od.items()))
            self.assertEqual(len(dup), len(od))
            self.assertEqual(type(dup), type(od))
        check(od.copy())
        check(copy.copy(od))
        check(copy.deepcopy(od))
        # pickle directly pulls the module, so we have to fake it
        with replaced_module('collections', self.module):
            for proto in range(pickle.HIGHEST_PROTOCOL + 1):
                with self.subTest(proto=proto):
                    check(pickle.loads(pickle.dumps(od, proto)))
        check(eval(repr(od)))
        update_test = OrderedDict()
        update_test.update(od)
        check(update_test)
        check(OrderedDict(od)) 

def test_multiset_operations(self):
        # Verify that adding a zero counter will strip zeros and negatives
        c = Counter(a=10, b=-2, c=0) + Counter()
        self.assertEqual(dict(c), dict(a=10))

        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for counterop, numberop in [
                (Counter.__add__, lambda x, y: max(0, x+y)),
                (Counter.__sub__, lambda x, y: max(0, x-y)),
                (Counter.__or__, lambda x, y: max(0,x,y)),
                (Counter.__and__, lambda x, y: max(0, min(x,y))),
            ]:
                result = counterop(p, q)
                for x in elements:
                    self.assertEqual(numberop(p[x], q[x]), result[x],
                                     (counterop, x, p, q))
                # verify that results exclude non-positive counts
                self.assertTrue(x>0 for x in result.values())

        elements = 'abcdef'
        for i in range(100):
            # verify that random multisets with no repeats are exactly like sets
            p = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            q = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            for counterop, setop in [
                (Counter.__sub__, set.__sub__),
                (Counter.__or__, set.__or__),
                (Counter.__and__, set.__and__),
            ]:
                counter_result = counterop(p, q)
                set_result = setop(set(p.elements()), set(q.elements()))
                self.assertEqual(counter_result, dict.fromkeys(set_result, 1)) 

def test_update(self):
        c = Counter()
        c.update(self=42)
        self.assertEqual(list(c.items()), [('self', 42)])
        c = Counter()
        c.update(iterable=42)
        self.assertEqual(list(c.items()), [('iterable', 42)])
        c = Counter()
        c.update(iterable=None)
        self.assertEqual(list(c.items()), [('iterable', None)])
        self.assertRaises(TypeError, Counter().update, 42)
        self.assertRaises(TypeError, Counter().update, {}, {})
        self.assertRaises(TypeError, Counter.update) 

def test_update(self):
        c = Counter()
        c.update(self=42)
        self.assertEqual(list(c.items()), [('self', 42)])
        c = Counter()
        c.update(iterable=42)
        self.assertEqual(list(c.items()), [('iterable', 42)])
        c = Counter()
        c.update(iterable=None)
        self.assertEqual(list(c.items()), [('iterable', None)])
        self.assertRaises(TypeError, Counter().update, 42)
        self.assertRaises(TypeError, Counter().update, {}, {})
        self.assertRaises(TypeError, Counter.update) 

def test_update(self):
        with self.assertRaises(TypeError):
            OrderedDict().update([('a', 1), ('b', 2)], None)                        # too many args
        pairs = [('a', 1), ('b', 2), ('c', 3), ('d', 4), ('e', 5)]
        od = OrderedDict()
        od.update(dict(pairs))
        self.assertEqual(sorted(od.items()), pairs)                                 # dict input
        od = OrderedDict()
        od.update(**dict(pairs))
        self.assertEqual(sorted(od.items()), pairs)                                 # kwds input
        od = OrderedDict()
        od.update(pairs)
        self.assertEqual(list(od.items()), pairs)                                   # pairs input
        od = OrderedDict()
        od.update([('a', 1), ('b', 2), ('c', 9), ('d', 4)], c=3, e=5)
        self.assertEqual(list(od.items()), pairs)                                   # mixed input

        # Issue 9137: Named argument called 'other' or 'self'
        # shouldn't be treated specially.
        od = OrderedDict()
        od.update(self=23)
        self.assertEqual(list(od.items()), [('self', 23)])
        od = OrderedDict()
        od.update(other={})
        self.assertEqual(list(od.items()), [('other', {})])
        od = OrderedDict()
        od.update(red=5, blue=6, other=7, self=8)
        self.assertEqual(sorted(list(od.items())),
                         [('blue', 6), ('other', 7), ('red', 5), ('self', 8)])

        # Make sure that direct calls to update do not clear previous contents
        # add that updates items are not moved to the end
        d = OrderedDict([('a', 1), ('b', 2), ('c', 3), ('d', 44), ('e', 55)])
        d.update([('e', 5), ('f', 6)], g=7, d=4)
        self.assertEqual(list(d.items()),
            [('a', 1), ('b', 2), ('c', 3), ('d', 4), ('e', 5), ('f', 6), ('g', 7)])

        self.assertRaises(TypeError, OrderedDict().update, 42)
        self.assertRaises(TypeError, OrderedDict().update, (), ())
        self.assertRaises(TypeError, OrderedDict.update) 

def test_update(self):
        c = Counter()
        c.update(self=42)
        self.assertEqual(list(c.items()), [('self', 42)])
        c = Counter()
        c.update(iterable=42)
        self.assertEqual(list(c.items()), [('iterable', 42)])
        c = Counter()
        c.update(iterable=None)
        self.assertEqual(list(c.items()), [('iterable', None)])
        self.assertRaises(TypeError, Counter().update, 42)
        self.assertRaises(TypeError, Counter().update, {}, {})
        self.assertRaises(TypeError, Counter.update) 

def test_multiset_operations(self):
        # Verify that adding a zero counter will strip zeros and negatives
        c = Counter(a=10, b=-2, c=0) + Counter()
        self.assertEqual(dict(c), dict(a=10))

        elements = 'abcd'
        for i in range(1000):
            # test random pairs of multisets
            p = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            p.update(e=1, f=-1, g=0)
            q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
            q.update(h=1, i=-1, j=0)
            for counterop, numberop in [
                (Counter.__add__, lambda x, y: max(0, x+y)),
                (Counter.__sub__, lambda x, y: max(0, x-y)),
                (Counter.__or__, lambda x, y: max(0,x,y)),
                (Counter.__and__, lambda x, y: max(0, min(x,y))),
            ]:
                result = counterop(p, q)
                for x in elements:
                    self.assertEqual(numberop(p[x], q[x]), result[x],
                                     (counterop, x, p, q))
                # verify that results exclude non-positive counts
                self.assertTrue(x>0 for x in result.values())

        elements = 'abcdef'
        for i in range(100):
            # verify that random multisets with no repeats are exactly like sets
            p = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            q = Counter(dict((elem, randrange(0, 2)) for elem in elements))
            for counterop, setop in [
                (Counter.__sub__, set.__sub__),
                (Counter.__or__, set.__or__),
                (Counter.__and__, set.__and__),
            ]:
                counter_result = counterop(p, q)
                set_result = setop(set(p.elements()), set(q.elements()))
                self.assertEqual(counter_result, dict.fromkeys(set_result, 1)) 

def test_copying(self):
        # Check that counters are copyable, deepcopyable, picklable, and
        #have a repr/eval round-trip
        words = Counter('which witch had which witches wrist watch'.split())
        update_test = Counter()
        update_test.update(words)
        for i, dup in enumerate([
                    words.copy(),
                    copy.copy(words),
                    copy.deepcopy(words),
                    pickle.loads(pickle.dumps(words, 0)),
                    pickle.loads(pickle.dumps(words, 1)),
                    pickle.loads(pickle.dumps(words, 2)),
                    pickle.loads(pickle.dumps(words, -1)),
                    cPickle.loads(cPickle.dumps(words, 0)),
                    cPickle.loads(cPickle.dumps(words, 1)),
                    cPickle.loads(cPickle.dumps(words, 2)),
                    cPickle.loads(cPickle.dumps(words, -1)),
                    eval(repr(words)),
                    update_test,
                    Counter(words),
                    ]):
            msg = (i, dup, words)
            self.assertTrue(dup is not words)
            self.assertEqual(dup, words)
            self.assertEqual(len(dup), len(words))
            self.assertEqual(type(dup), type(words))