无法通过exec()语句更改函数中的全局变量? [英] Cannot change global variables in a function through an exec() statement?

问题描述

为什么我不能使用exec()从函数内部更改全局变量?当赋值语句在exec()之外时，它可以正常工作.这是我的问题的一个示例:

Why can I not change global variables from inside a function, using exec()? It works fine when the assignment statement is outside of exec(). Here is an example of my problem:

>>> myvar = 'test'
>>> def myfunc():
...     global myvar
...     exec('myvar = "changed!"')
...     print(myvar)
... 
>>> myfunc()
test
>>> print(myvar)
test

推荐答案

每 docs ，exec语句采用两个可选表达式，默认为globals()和locals()，并且始终在locals()中执行更改(如果有).

Per the docs, the exec statement takes two optional expressions, defaulting to globals() and locals(), and always performs changes (if any) in the locals() one.

因此，请更加明确/具体/精确...:

So, just be more explicit/specific/precise...:

>>> def myfunc():
...   exec('myvar="boooh!"', globals())
... 
>>> myfunc()
>>> myvar
'boooh!'

...，您将可以将全局变量破坏到您的内心.

...and you'll be able to clobber global variables to your heart's contents.

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