Simplify Counter() API. Replace items keyword argument
with a mapping. Makes Counter() idempotent, makes update()
API the same as Counter.__init__(), makes a more readable
repr, makes the API more dict-like, and allows Steven
Bethard's update() example to work.
diff --git a/Lib/collections.py b/Lib/collections.py
index ff49844..349f884 100644
--- a/Lib/collections.py
+++ b/Lib/collections.py
@@ -167,21 +167,17 @@
# http://code.activestate.com/recipes/259174/
# Knuth, TAOCP Vol. II section 4.6.3
- def __init__(self, iterable=None, items=None):
+ def __init__(self, iterable=None):
'''Create a new, empty Counter object. And if given, count elements
- from an input iterable. Or, initialize the count from an items list
- of (element, count) pairs.
+ from an input iterable. Or, initialize the count from another mapping
+ of elements to their counts.
- >>> c = Counter('hocus pocus') # count elements in an iterable
- >>> c = Counter(items=[('a', 4), ('b', 2)]) # take counts from an items list
+ >>> c = Counter() # a new, empty counter
+ >>> c = Counter('hocus pocus') # a new counter from an iterable
+ >>> c = Counter({'a': 4, 'b': 2}) # a new counter from a mapping
'''
- if iterable is not None:
- for elem in iterable:
- self[elem] += 1
- if items is not None:
- for elem, count in items:
- self[elem] += count
+ self.update(iterable)
def __missing__(self, key):
'The count of elements not in the Counter is zero.'
@@ -210,7 +206,7 @@
# Knuth's example of prime factors of 1836: 2**2 * 3**3 * 17**1
>>> import operator
- >>> prime_factors = Counter(items=[(2,2), (3,3), (17,1)])
+ >>> prime_factors = Counter(dict([(2,2), (3,3), (17,1)]))
>>> sorted(prime_factors.elements()) # list individual factors
[2, 2, 3, 3, 3, 17]
>>> reduce(operator.mul, prime_factors.elements(), 1) # multiply them
@@ -234,16 +230,19 @@
raise NotImplementedError(
'Counter.fromkeys() is undefined. Use Counter(iterable) instead.')
- def update(self, mapping):
+ def update(self, iterable=None):
'''Like dict.update() but add counts instead of replacing them.
- Source can be another dictionary or a Counter.instance().
+ Source can be an iterable, a dictionary, or another Counter.instance().
>>> c = Counter('which')
>>> d = Counter('witch')
- >>> c.update(d) # Add counts from d to those in c
- >>> c['h'] # Count of 'h' is now three
+ >>> c.update(d) # add counts from d to those in c
+ >>> c['h'] # count of 'h' is now three
3
+ >>> c.update('watch')
+ >>> c['h']
+ 4
'''
# The regular dict.update() operation makes no sense here because the
@@ -254,19 +253,24 @@
# multisets and implement the union-add operation discussed in
# TAOCP Volume II section 4.6.3 exercise 19. The Wikipedia entry for
# multisets calls that operation a sum or join.
- for elem, count in mapping.iteritems():
- self[elem] += count
+
+ if iterable is not None:
+ if isinstance(iterable, Mapping):
+ for elem, count in iterable.iteritems():
+ self[elem] += count
+ else:
+ for elem in iterable:
+ self[elem] += 1
def copy(self):
'Like dict.copy() but returns a Counter instance instead of a dict.'
- c = Counter()
- c.update(self)
- return c
+ return Counter(self)
def __repr__(self):
if not self:
return '%s()' % self.__class__.__name__
- return '%s(items=%r)' % (self.__class__.__name__, self.most_common())
+ items = ', '.join('%r: %r' % item for item in self.most_common())
+ return '%s({%s})' % (self.__class__.__name__, items)