dict.items（）和dict.iteritems（）有什么区别？ [英] What is the difference between dict.items() and dict.iteritems()?

问题描述

dict.items（ ） 和 dict.iteritems（） ？

从Python文档：

dict.items（）：返回字典的（键，值）对列表的复制。

dict.items(): Return a copy of the dictionary’s list of (key, value) pairs.

dict.iteritems（）：返回一个迭代器值）对。

如果我运行下面的代码，每个似乎都返回对同一个对象的引用。有没有什么微妙的差异，我失踪了？

If I run the code below, each seems to return a reference to the same object. Are there any subtle differences that I am missing?

#!/usr/bin/python

d={1:'one',2:'two',3:'three'}
print 'd.items():'
for k,v in d.items():
   if d[k] is v: print '\tthey are the same object' 
   else: print '\tthey are different'

print 'd.iteritems():'   
for k,v in d.iteritems():
   if d[k] is v: print '\tthey are the same object' 
   else: print '\tthey are different'   

输出：

d.items():
    they are the same object
    they are the same object
    they are the same object
d.iteritems():
    they are the same object
    they are the same object
    they are the same object

推荐答案

这是进化的一部分。

最初，Python items（）构建了一个真正的元组列表，并返回。这可能需要很多额外的记忆。

Originally, Python items() built a real list of tuples and returned that. That could potentially take a lot of extra memory.

然后，生成器一般被引入到语言中，该方法被重新实现为一个名为 iteritems（）。原始版本保持向后兼容性。

Then, generators were introduced to the language in general, and that method was reimplemented as an iterator-generator method named iteritems(). The original remains for backwards compatibility.

Python 3的更改之一是 items（）现在返回迭代器，并且一个列表从未完全构建。 iteritems（）方法也没有了，因为Python 3中的 items（）类似于 viewitems（）在Python 2.7中。

One of Python 3’s changes is that items() now return iterators, and a list is never fully built. The iteritems() method is also gone, since items() in Python 3 works like viewitems() in Python 2.7.

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