Build-outs for Counter() class:
* Constructor and update() support keyword args (like their dict counterparts).
* The 'del' statement no longer raises KeyError for missing values.
* Add multiset operations: __add__, __sub__, __and__, __or__.
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 13ae9bf..ddf8398 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -2,6 +2,8 @@
from test import test_support
from collections import namedtuple, Counter, Mapping
import pickle, cPickle, copy
+from random import randrange
+import operator
from collections import Hashable, Iterable, Iterator
from collections import Sized, Container, Callable
from collections import Set, MutableSet
@@ -350,6 +352,8 @@
def test_basics(self):
c = Counter('abcaba')
+ self.assertEqual(c, Counter({'a':3 , 'b': 2, 'c': 1}))
+ self.assertEqual(c, Counter(a=3, b=2, c=1))
self.assert_(isinstance(c, dict))
self.assert_(isinstance(c, Mapping))
self.assert_(issubclass(Counter, dict))
@@ -379,6 +383,7 @@
c['a'] += 1 # increment an existing value
c['b'] -= 2 # sub existing value to zero
del c['c'] # remove an entry
+ del c['c'] # make sure that del doesn't raise KeyError
c['d'] -= 2 # sub from a missing value
c['e'] = -5 # directly assign a missing value
c['f'] += 4 # add to a missing value
@@ -394,7 +399,8 @@
self.assertEqual(repr(c), 'Counter()')
self.assertRaises(NotImplementedError, Counter.fromkeys, 'abc')
self.assertRaises(TypeError, hash, c)
- c.update(dict(a=5, b=3, c=1))
+ c.update(dict(a=5, b=3))
+ c.update(c=1)
c.update(Counter('a' * 50 + 'b' * 30))
c.update() # test case with no args
c.__init__('a' * 500 + 'b' * 300)
@@ -442,6 +448,43 @@
self.assertEqual(dict(Counter(s)), dict(Counter(s).items()))
self.assertEqual(set(Counter(s)), set(s))
+ 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))
+ q = Counter(dict((elem, randrange(-2,4)) for elem in elements))
+ for counterop, numberop, defneg in [
+ (Counter.__add__, lambda x, y: x+y if x+y>0 else 0, True),
+ (Counter.__sub__, lambda x, y: x-y if x-y>0 else 0, False),
+ (Counter.__or__, max, False),
+ (Counter.__and__, min, False),
+ ]:
+ result = counterop(p, q)
+ for x in elements:
+ # all except __add__ are undefined for negative inputs
+ if defneg or (p[x] >= 0 and q[x] >= 0):
+ self.assertEqual(numberop(p[x], q[x]), result[x])
+ # verify that results exclude non-positive counts
+ self.assert_(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))
import doctest, collections