python中的collections模块

>>> c = Counter('abcdeabcdabcaba')  # count elements from a string
 |  
 |  >>> c.most_common(3)                # three most common elements
 |  [('a', 5), ('b', 4), ('c', 3)]
 |  >>> sorted(c)                       # list all unique elements
 |  ['a', 'b', 'c', 'd', 'e']
 |  >>> ''.join(sorted(c.elements()))   # list elements with repetitions
 |  'aaaaabbbbcccdde'
 |  >>> sum(c.values())                 # total of all counts
 |  15
 |  
 |  >>> c['a']                          # count of letter 'a'
 |  5
 |  >>> for elem in 'shazam':           # update counts from an iterable
 |  ...     c[elem] += 1                # by adding 1 to each element's count
 |  >>> c['a']                          # now there are seven 'a'
 |  7
 |  >>> del c['b']                      # remove all 'b'
 |  >>> c['b']                          # now there are zero 'b'
 |  0
 |  
 |  >>> d = Counter('simsalabim')       # make another counter
 |  >>> c.update(d)                     # add in the second counter
 |  >>> c['a']                          # now there are nine 'a'
 |  9
 |  
 |  >>> c.clear()                       # empty the counter
 |  >>> c
 |  Counter()