Python中的全局和局部变量 [英] Global and local variables in Python

问题描述

我正在学习Python。一本关于Python 3的书说以下代码应该可以正常工作：

I am learning Python. A book on Python 3 says the following code should work fine:

def funky():
    print(myvar)
    myvar = 20
    print(myvar)

myvar = 10
funky()

但是当我在Python 3.3中运行它时，我得到了

But when I run it in Python 3.3, I got the

UnboundLocalError: local variable 'myvar' referenced before assignment

错误。我的理解是， funky 中的第一个 print（myvar）应该是10，因为它是一个全局变量。第二个 print（myvar）应该是20，因为本地 myvar 被定义为20.这里是怎么回事？请帮助澄清。

error. My understanding is that the first print(myvar) in funky should be 10 since it's a global variable. The second print(myvar) should be 20 since a local myvar is defined to be 20. What is going on here? Please help clarify.

推荐答案

您需要在函数中调用 global

You need to call global in your function before assigning a value.

def funky():
    global myvar
    print(myvar)
    myvar = 20
    print(myvar)

myvar = 10
funky()

请注意，您可以在不调用全局的情况下打印该值，因为您可以在不使用 global 的情况下访问全局变量，但尝试分配值需要它。

Note that you can print the value without calling global because you can access global variables without using global, but attempting to assign a value will require it.

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