Python Collections

24cun_cn

Collections
High-performance container datatypes
   * nametuple()
   * deque
   * Counter
   * OrderedDict
   * defaultdict
一、Counter
dict subclass for counting hash able objects


Python 2.7.2 (default, Jun 20 2012, 16:23:33)
[GCC 4.2.1 Compatible Apple Clang 4.0 (tags/Apple/clang-418.0.60)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from collections import Counter
>>> cnt = Counter()
>>> dir(cnt)
['__add__', '__and__', '__class__', '__cmp__', '__contains__', '__delattr__', '__delitem__', '__dict__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__missing__', '__module__', '__ne__', '__new__', '__or__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__weakref__', 'clear', 'copy', 'elements', 'fromkeys', 'get', 'has_key', 'items', 'iteritems', 'iterkeys', 'itervalues', 'keys', 'most_common', 'pop', 'popitem', 'setdefault', 'subtract', 'update', 'values', 'viewitems', 'viewkeys', 'viewvalues']

>>> for word in ['red', 'blue', 'red', 'green', 'blue', 'blue']:
...     cnt[word] += 1
...
>>> cnt
Counter({'blue': 6, 'red': 4, 'green': 2})



1、elements

>>> list(cnt.elements())
['blue', 'blue', 'blue', 'blue', 'blue', 'blue', 'green', 'green', 'red', 'red', 'red', 'red']



2、most_common([n])

>>> cnt.most_common(3);
[('blue', 6), ('red', 4), ('green', 2)]


3、subtract

>>> cnt2=Counter(blue=1,red=2)
>>> cnt.subtract(cnt2)
>>> cnt
Counter({'blue': 5, 'green': 2, 'red': 2, 'orange': 1})



4、fromkeys
not implemented.

5、update

>>> cnt.update({'orange'})
>>> cnt
Counter({'blue': 6, 'red': 4, 'green': 2, 'orange': 1})




二、deque


>>> from collections import deque
>>> dir(deque)
['__class__', '__copy__', '__delattr__', '__delitem__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'appendleft', 'clear', 'count', 'extend', 'extendleft', 'maxlen', 'pop', 'popleft', 'remove', 'reverse', 'rotate']



1、append
2、appendleft(x)
3、clear
4、count(x)
5、extend(iterable)
6、extendleft(iterable)
7、pop()
8、popleft()
9、remove(value)
10、reverse()
11、rotate(n)
12、maxlen

三、defaultdict

dict's subclass
使用defaultdict方法可以轻松定义一个树的数据结构


from collections import defaultdict
import simplejson as json
def tree():
return defaultdict(tree)

def dicts(t):
return {k: dicts(t[k]) for k in t}  if isinstance(t, defaultdict) else t

users = tree()
users['good']['username']='eric'
users['bad']['username']='ricky'
print (json.dumps(users))
print dicts(users)



{"bad": {"username": "ricky"}, "good": {"username": "eric"}}
{'bad': {'username': 'ricky'}, 'good': {'username': 'eric'}}



四、namedtuple

from collections import named tuple
Point = namedtuple('Point','x y',verbose=True)
point = Point(1,2)
print point

class Point(tuple):
'Point(x, y)'
__slots__ = ()
_fields = ('x', 'y')
def __new__(_cls, x, y):
'Create new instance of Point(x, y)'
return _tuple.__new__(_cls, (x, y))
@classmethod
def _make(cls, iterable, new=tuple.__new__, len=len):
'Make a new Point object from a sequence or iterable'
result = new(cls, iterable)
if len(result) != 2:
raise TypeError('Expected 2 arguments, got %d' % len(result))
return result
def __repr__(self):
'Return a nicely formatted representation string'
return 'Point(x=%r, y=%r)' % self
def _asdict(self):
'Return a new OrderedDict which maps field names to their values'
return OrderedDict(zip(self._fields, self))
def _replace(_self, **kwds):
'Return a new Point object replacing specified fields with new values'
result = _self._make(map(kwds.pop, ('x', 'y'), _self))
if kwds:
raise ValueError('Got unexpected field names: %r' % kwds.keys())
return result
def __getnewargs__(self):
'Return self as a plain tuple.  Used by copy and pickle.'
return tuple(self)
x = _property(_itemgetter(0), doc='Alias for field number 0')
y = _property(_itemgetter(1), doc='Alias for field number 1')


五、OrderedDict

In [15]: from collections import OrderedDict

In [16]: d = {'banana': 3, 'apple':4, 'pear': 1, 'orange': 2}

In [17]: OrderedDict(sorted(d.items(), key=lambda t: t[0]))
Out[17]: OrderedDict([('apple', 4), ('banana', 3), ('orange', 2), ('pear', 1)])

In [18]: OrderedDict(sorted(d.items(), key=lambda t: t[1]))
Out[18]: OrderedDict([('pear', 1), ('orange', 2), ('banana', 3), ('apple', 4)])

In [19]: OrderedDict(sorted(d.items(), key=lambda t: len(t[0])))
Out[19]: OrderedDict([('pear', 1), ('apple', 4), ('orange', 2), ('banana', 3)])



参考资料:
http://docs.python.org/2/library/collections.html