访问调用函数的变量

The following code

以下代码

class Foo(object):
    def do_something(self):
        print(main.func_code.co_varnames)
        for item in main.func_code.co_varnames:
            eval(item)

def main():
    a = 1
    b = Foo()
    b.do_something()

main()

will print

('a', 'b')

along with an error message ending with

以及以。结尾的错误消息

name 'a' is not defined

Somehow a Foo object is able to get the names of another function's local variables, but cannot do anything with them. How can I fix that?

不知何故,Foo对象能够获取另一个函数的局部变量的名称,但不能对它们做任何事情。我该如何解决这个问题?

BACKGROUND. This question is for debugging purposes. I want to be able to display information about variables that are created in my code.

背景。这个问题是出于调试目的。我希望能够显示有关在我的代码中创建的变量的信息。

2 个解决方案

#1

The local variables are defined for the function. So as long as the function is defined, the interpreter "knows" that there will be 2 local variables, named a and b. Useful for memory allocation, when the function will be called. Think of it as a blueprint.

为函数定义局部变量。因此,只要定义了函数,解释器就“知道”将有2个局部变量,名为a和b。当函数被调用时,对内存分配很有用。把它想象成一幅蓝图。

Then, when you try to eval some string, it will do it using the context (locals() and globals()) of where the eval lies. You do not have any a in that scope. Therefore, it fails, as it is not defined.

然后,当你尝试eval一些字符串时,它将使用eval所在的上下文(locals()和globals())来完成它。你在那个范围内没有任何一个。因此,它失败了,因为它没有定义。

#2

Use inspect.currentframe to get a stack frame object

使用inspect.currentframe获取堆栈帧对象

Move up the call stack by 1 frame with the f_back attribute

使用f_back属性将调用堆栈向上移动1帧

Access that frame's local variables through the f_locals attribute

通过f_locals属性访问该框架的局部变量

import inspect

def get_variables():
    frame = inspect.currentframe().f_back
    print(frame.f_locals)

Usage:

def main():
    a = 1
    b = 'hello world'

    get_variables()

main()
# output: {'b': 'hello world', 'a': 1}

#1