python collections模块

collections模块基本介绍

collections在通用的容器dict,list,set和tuple之上提供了几个可选的数据类型

namedtuple()	factory function for creating tuple subclasses with named fields
deque	list-like container with fast appends and pops on either end
ChainMap	dict-like class for creating a single view of multiple mappings
Counter	dict subclass for counting hashable objects
OrderedDict	dict subclass that remembers the order entries were added
defaultdict	dict subclass that calls a factory function to supply missing values
UserDict	wrapper around dictionary objects for easier dict subclassing
UserList	wrapper around list objects for easier list subclassing
UserString	wrapper around string objects for easier string subclassing

namedtuple()

tuple类似于数组，只能通过下表来访问各个元素。使用namedtuple，每个元素有自己的名字，数据的意义一目了然。

In [22]: from collections import namedtuple

In [23]: Point = namedtuple('Point', ['x', 'y'])

In [24]: p = Point(11, y=22)

In [25]: p[0] + p[1]
Out[25]: 33

In [26]: p.x
Out[26]: 11

In [27]: p.y
Out[27]: 22

In [28]: p
Out[28]: Point(x=11, y=22)

In [29]: x, y = p

In [30]: x
Out[30]: 11

命名元组还有三种额外的方法，两个属性

classmethod somenamedtuple._make(iterable)

　　Class method that makes a new instance from an existing sequence or iterable.

　　从一个已经存在的序列或可迭代对象创建一个新实例

In [1]: from collections import namedtuple

In [2]: Point = namedtuple('Point', ['x', 'y', 'z'])

In [3]: t = [1, 2, 3]

In [4]: p = Point._make(t)

In [5]: p
Out[5]: Point(x=1, y=2, z=3)

somenamedtuple._asdict()

　　Return a new OrderedDict which maps field names to their corresponding values:

　　返回一个新的OrderedDict，并以field names作为key， field names对应值作为values。

In [16]: from collections import namedtuple

In [17]: Point = namedtuple('Point', ['x', 'y', 'z'])

In [18]: t = [1, 2, 3]

In [19]: p = Point._make(t)

In [20]: p
Out[20]: Point(x=1, y=2, z=3)

In [21]: d = p._asdict()

In [22]: d.get('x')
Out[22]: 1

In [23]: d
Out[23]: OrderedDict([('x', 1), ('y', 2), ('z', 3)])

somenamedtuple._replace(kwargs)

　　Return a new instance of the named tuple replacing specified fields with new values:

　　返回一个用新值替换指定字段后的命名元组的一个新实例。

In [24]: from collections import namedtuple

In [25]: Point = namedtuple('Point', ['x', 'y', 'z'])

In [26]: t = [1, 2, 3]

In [27]: p = Point._make(t)

In [28]: p
Out[28]: Point(x=1, y=2, z=3)

In [29]: p._replace(z=4)
Out[29]: Point(x=1, y=2, z=4)

In [30]: p.z
Out[30]: 3

In [31]: p = p._replace(z=4)

In [33]: p.z
Out[33]: 4

In [34]: p
Out[34]: Point(x=1, y=2, z=4)

somenamedtuple._fields

　　Tuple of strings listing the field names. Useful for introspection and for creating new named tuple types from existing named tuples.

　　字段名列表

In [35]: p._fields
Out[35]: ('x', 'y', 'z')

somenamedtuple._source

　　A string with the pure Python source code used to create the named tuple class. The source makes the named tuple self-documenting. It can be printed, executed using exec(), or saved to a file and imported.

　　创建命名元组的纯python代码

In [36]: p._source
Out[36]: "from builtins import property as _property, tuple as _tuple\nfrom operator import itemgetter as _itemgetter\nfrom collections import OrderedDict\n\nclass Point(tuple):\n    'Point(x, y, z)'\n\n    __slots__ = ()\n\n    _fields = ('x', 'y', 'z')\n\n    def __new__(_cls, x, y, z):\n        'Create new instance of Point(x, y, z)'\n        return _tuple.__new__(_cls, (x, y, z))\n\n    @classmethod\n    def _make(cls, iterable, new=tuple.__new__, len=len):\n        'Make a new Point object from a sequence or iterable'\n        result = new(cls, iterable)\n        if len(result) != 3:\n            raise TypeError('Expected 3 arguments, got %d' % len(result))\n        return result\n\n    def _replace(_self, **kwds):\n        'Return a new Point object replacing specified fields with new values'\n        result = _self._make(map(kwds.pop, ('x', 'y', 'z'), _self))\n        if kwds:\n            raise ValueError('Got unexpected field names: %r' % list(kwds))\n        return result\n\n    def __repr__(self):\n        'Return a nicely formatted representation string'\n        return self.__class__.__name__ + '(x=%r, y=%r, z=%r)' % self\n\n    def _asdict(self):\n        'Return a new OrderedDict which maps field names to their values.'\n        return OrderedDict(zip(self._fields, self))\n\n    def __getnewargs__(self):\n        'Return self as a plain tuple.  Used by copy and pickle.'\n        return tuple(self)\n\n    x = _property(_itemgetter(0), doc='Alias for field number 0')\n\n    y = _property(_itemgetter(1), doc='Alias for field number 1')\n\n    z = _property(_itemgetter(2), doc='Alias for field number 2')\n\n"

OrderedDict()

　　字典都是是无序的，通过OrderedDict创建的字典会记住插入的顺序。

In [40]: from collections import OrderedDict

In [41]: hexm = {'name': 'hexiaoming', 'age': 15, 'sexy': 'male'}

In [42]: dict(hexm)
Out[42]: {'age': 15, 'name': 'hexiaoming', 'sexy': 'male'}

In [43]: OrderedDict(hexm)
Out[43]: OrderedDict([('name', 'hexiaoming'), ('age', 15), ('sexy', 'male')])

In [44]: d1 = OrderedDict(hexm)

In [45]: d1['eat'] = 'gousi'

In [46]: d1
Out[46]:
　　OrderedDict([('name', 'hexiaoming'),
　　　　('age', 15),
　　　　('sexy', 'male'),
　　　　('eat', 'gousi')])

　　对字典排序：

In [47]: d = {'banana': 3, 'apple': 4, 'pear': 1, 'orange': 2}

In [48]: OrderedDict(sorted(d.items(), key=lambda t: t[0]))
Out[48]: OrderedDict([('apple', 4), ('banana', 3), ('orange', 2), ('pear', 1)])

In [49]: OrderedDict(sorted(d.items(), key=lambda t: t[1]))
Out[49]: OrderedDict([('pear', 1), ('orange', 2), ('banana', 3), ('apple', 4)])

In [50]: OrderedDict(sorted(d.items(), key=lambda t: len(t[0])))
Out[50]: OrderedDict([('pear', 1), ('apple', 4), ('banana', 3), ('orange', 2)])