[英]Python3 `builtins` is not always `__builtins__`
I was putting this idea How to make a cross-module variable?我提出了这个想法如何制作跨模块变量? in action for python3.在 python3 中运行。 And was lazy enough to use the variable __builtins__
instead of the module builtins
.并且懒得使用变量__builtins__
而不是模块builtins
。 Which should make no difference because:这应该没有区别,因为:
# file spam.py:
import builtins
print (builtins is __builtins__)
print (id(builtins))
print (id(__builtins__))
This is when it gets funny: builtins
is not __builtins__
when imported:这是有趣的时候: builtins
函数在导入时不是__builtins__
:
$ python3 spam.py
True
140598001743336
140598001743336
$ python3 -c 'import spam'
False
139755426543080
139755426520904
Does anyone know what happens?有谁知道会发生什么?
(A comment on the given page mentions " __builtins__
is a CPython peculiarity, you really shouldn't use it", but I'm being curious...) (给定页面上的评论提到“ __builtins__
是 CPython 的特性,你真的不应该使用它”,但我很好奇......)
I don't really know why, but from article我真的不知道为什么,但从文章
frame globals have a
__builtins__
variable (builtins dictionary, or builtins module when__name__
equals__main__
)框架全局变量有一个__builtins__
变量(当__name__
等于__main__
时,内置字典或内置模块)
so in your first case ( __name__ == __main__
) and you get __builtins__
as builtins
module, but in the second case ( __name__ != __main__
) __builtins__
is a dict
instance and from docs :所以在你的第一种情况下( __name__ == __main__
),你得到__builtins__
作为builtins
模块,但在第二种情况下( __name__ != __main__
) __builtins__
是一个dict
实例,来自docs :
The value of
__builtins__
is normally either this module or the value of this module's__dict__
attribute.__builtins__
的值通常是这个模块或者这个模块的__dict__
属性的值。
With slightly modified spam.py
稍微修改spam.py
import builtins
if __name__ == '__main__':
print(type(__builtins__))
print(__builtins__ is builtins)
print(id(builtins))
print(id(__builtins__))
else:
print(type(__builtins__))
print(__builtins__ is builtins.__dict__)
print(id(builtins.__dict__))
print(id(__builtins__))
we will get something like我们会得到类似的东西
$ python3 spam.py
<class 'module'>
True
2345652270648
2345652270648
$ python3 -c 'import spam'
<class 'dict'>
True
2770543697736
2770543697736
As you & @chepner have already noticed __builtins__
is an implementation detail that can be changed, so we shouldn't rely on it, especially on it being a builtins
module/ builtins.__dict__
object.正如你和@chepner 已经注意到__builtins__
是一个可以改变的实现细节,所以我们不应该依赖它,尤其是它是一个builtins
module/ builtins.__dict__
对象。
For CPython implementation,对于 CPython 实现,
in the __main__
module: __builtins__ is builtins
.在__main__
模块中: __builtins__ is builtins
。
in other module: __builtins__ is builtins.__dict__
在其他模块中: __builtins__ is builtins.__dict__
Refs:参考:
https://docs.python.org/3/reference/executionmodel.html#builtins-and-restricted-executionhttp://mathamy.com/whats-the-deal-with-builtins-vs-builtin.html https://docs.python.org/3/reference/executionmodel.html#builtins-and-restricted-executionhttp://mathamy.com/whats-the-deal-with-builtins-vs-builtin.html
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