Python中内建模块collections如何使用

>>> p = (1, 2)

>>> from collections import namedtuple
>>> Point = namedtuple('Point', ['x', 'y'])
>>> p = Point(1, 2)
>>> p.x
1
>>> p.y
2

>>> isinstance(p, Point)
True
>>> isinstance(p, tuple)
True

# namedtuple('名称', [属性list]):
Circle = namedtuple('Circle', ['x', 'y', 'r'])

>>> from collections import deque
>>> q = deque(['a', 'b', 'c'])
>>> q.append('x')
>>> q.appendleft('y')
>>> q
deque(['y', 'a', 'b', 'c', 'x'])

>>> from collections import defaultdict
>>> dd = defaultdict(lambda: 'N/A')
>>> dd['key1'] = 'abc'
>>> dd['key1'] # key1存在
'abc'
>>> dd['key2'] # key2不存在，返回默认值
'N/A'

>>> from collections import OrderedDict
>>> d = dict([('a', 1), ('b', 2), ('c', 3)])
>>> d # dict的Key是无序的
{'a': 1, 'c': 3, 'b': 2}
>>> od = OrderedDict([('a', 1), ('b', 2), ('c', 3)])
>>> od # OrderedDict的Key是有序的
OrderedDict([('a', 1), ('b', 2), ('c', 3)])

>>> od = OrderedDict()
>>> od['z'] = 1
>>> od['y'] = 2
>>> od['x'] = 3
>>> od.keys() # 按照插入的Key的顺序返回
['z', 'y', 'x']

from collections import OrderedDict
class LastUpdatedOrderedDict(OrderedDict):
 def __init__(self, capacity):
  super(LastUpdatedOrderedDict, self).__init__()
  self._capacity = capacity
 def __setitem__(self, key, value):
  containsKey = 1 if key in self else 0
  if len(self) - containsKey >= self._capacity:
   last = self.popitem(last=False)
   print 'remove:', last
  if containsKey:
   del self[key]
   print 'set:', (key, value)
  else:
   print 'add:', (key, value)
  OrderedDict.__setitem__(self, key, value)

>>> from collections import Counter
>>> c = Counter()
>>> for ch in 'programming':
...  c[ch] = c[ch] + 1
...
>>> c
Counter({'g': 2, 'm': 2, 'r': 2, 'a': 1, 'i': 1, 'o': 1, 'n': 1, 'p': 1})