python namedtuple(命名元组)

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()

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"