Counter objects

---

A counter tool is provided to support convenient and rapid tallies. For example:

>>> # Tally occurrences of words in a list
>>> cnt = Counter()
>>> for word in ['red', 'blue', 'red', 'green', 'blue', 'blue']:
...     cnt[word] += 1
>>> cnt
Counter({'blue': 3, 'red': 2, 'green': 1})

>>> # Find the ten most common words in Hamlet
>>> import re
>>> words = re.findall(r'\w+', open('hamlet.txt').read().lower())
>>> Counter(words).most_common(10)
[('the', 1143), ('and', 966), ('to', 762), ('of', 669), ('i', 631),
 ('you', 554),  ('a', 546), ('my', 514), ('hamlet', 471), ('in', 451)]

class collections.Counter([iterable-or-mapping])

A Counter is a dict subclass for counting hashable objects. It is an unordered collection where elements are stored as dictionary keys and their counts are stored as dictionary values. Counts are allowed to be any integer value including zero or negative counts. The Counter class is similar to bags or multisets in other languages.

計數器是一個用於計算可雜湊物件的dict子類，它是一個無序的集合，其中的元素儲存為字典鍵，它們的計數儲存為字典值。它是一個無序的集合，其中元素被儲存為字典鍵，而它們的計數被儲存為字典值。計數可以是任何整數值，包括零或負數。Counter類類似於其他語言中的bag或multisets。

Elements are counted from an iterable or initialized from another mapping (or counter):元素的計數來自一個可迭代的或從另一個對映（或計數器）初始化的。

>>> c = Counter()                           # a new, empty counter
>>> c = Counter('gallahad')                 # a new counter from an iterable
>>> c = Counter({'red': 4, 'blue': 2})      # a new counter from a mapping
>>> c = Counter(cats=4, dogs=8)             # a new counter from keyword args

Counter objects have a dictionary interface except that they return a zero count for missing items instead of raising a KeyError:計數器物件有一個字典介面，除了它們對丟失的專案返回一個零計數，而不是引發一個KeyError。

>>> c = Counter(['eggs', 'ham'])
>>> c['bacon']                              # count of a missing element is zero
0

Setting a count to zero does not remove an element from a counter. Use del to remove it entirely:將計數設定為零並不會從計數器中刪除一個元素。使用del可以完全刪除它。

>>> c['sausage'] = 0                        # counter entry with a zero count
>>> del c['sausage']                        # del actually removes the entry