为什么在Python 3中将True和False更改为关键字 [英] Why were True and False changed to keywords in Python 3

问题描述

在Python 2中，我们可以重新分配True和False(但不能重新分配None)，但是三个(True，False和None)都被视为内置变量.但是，在Py3k中，根据文档将这三个变量都更改为关键字.. >

根据我自己的推测，我只能猜测这是为了防止像解决方案

可能是因为Python 2.6不仅允许True = False，而且还允许您说一些有趣的事情，例如:

__builtin__.True = False

，整个过程会将True重置为False.它可以导致发生真正有趣的事情:

>>> import __builtin__
>>> __builtin__.True = False
>>> True
False
>>> False
False
>>> __builtin__.False = True
>>> True
False
>>> False
False

编辑:如 Mike 所述，the docs.

From my own speculation, I could only guess that it was to prevent shenanigans like this which derive from the old True, False = False, True prank. However, in Python 2.7.5, and perhaps before, statements such as None = 3 which reassigned None raised SyntaxError: cannot assign to None.

Semantically, I don't believe True, False, and None are keywords, since they are at last semantically literals, which is what Java has done. I checked PEP 0 (the index) and I couldn't find a PEP explaining why they were changed.

Are there performance benefits or other reasons for making them keywords as opposed to literals or special-casing them like None in python2?

解决方案

Possibly because Python 2.6 not only allowed True = False but also allowed you to say funny things like:

__builtin__.True = False

which would reset True to False for the entire process. It can lead to really funny things happening:

>>> import __builtin__
>>> __builtin__.True = False
>>> True
False
>>> False
False
>>> __builtin__.False = True
>>> True
False
>>> False
False

EDIT: As pointed out by Mike, the Python wiki also states the following under Core Language Changes:

• Make True and False keywords.
  • Reason: make assignment to them impossible.

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