命名元組是如何在python內部實現的？

Question

命名元組很容易創建，輕量級對象類型。可以使用類似於對象的變量引用或標準元組語法來引用namedtuple實例。如果這些數據結構可以通過對象引用&索引來訪問，那麼它們是如何在內部實現的？它是通過哈希表嗎？

Answer 1

其實，這是很容易找出如何在給定namedtuple實現：如果您在創建時，它通過關鍵字參數verbose=True，其類定義打印：

>>> 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      This method is obsolete.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一個子類用一些額外的方法賦予它所需的行爲，包含字段名稱的_fields類級常量，以及用於對元組成員進行屬性訪問的方法。

至於實際構建這個類定義的代碼，那是deep magic。