命名元组是如何在python内部实现的？

Question

命名元组很容易创建，轻量级对象类型。可以使用类似于对象的变量引用或标准元组语法来引用namedtuple实例。如果这些数据结构可以通过对象引用&索引来访问，那么它们是如何在内部实现的？它是通过哈希表吗？

Answer 1

其实，这是很容易找出如何在给定namedtuple实现：如果您在创建时，它通过关键字参数verbose=True，其类定义打印：

>>> Point = namedtuple('Point', "x y", verbose=True) 
from builtins import property as _property, tuple as _tuple 
from operator import itemgetter as _itemgetter 
from collections import OrderedDict 

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 _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' % list(kwds)) 
     return result 

    def __repr__(self): 
     'Return a nicely formatted representation string' 
     return self.__class__.__name__ + '(x=%r, y=%r)' % self 

    @property 
    def __dict__(self): 
     'A new OrderedDict mapping field names to their values' 
     return OrderedDict(zip(self._fields, self)) 

    def _asdict(self): 
     '''Return a new OrderedDict which maps field names to their values. 
      This method is obsolete. Use vars(nt) or nt.__dict__ instead. 
     ''' 
     return self.__dict__ 

    def __getnewargs__(self): 
     'Return self as a plain tuple. Used by copy and pickle.' 
     return tuple(self) 

    def __getstate__(self): 
     'Exclude the OrderedDict from pickling' 
     return None 

    x = _property(_itemgetter(0), doc='Alias for field number 0') 

    y = _property(_itemgetter(1), doc='Alias for field number 1') 

因此，它的tuple一个子类用一些额外的方法赋予它所需的行为，包含字段名称的_fields类级常量，以及用于对元组成员进行属性访问的方法。

至于实际构建这个类定义的代码，那是deep magic。