在python模块中访问全局变量

Question

How do I access all global variables inside a module (I don't who they are in advance)?

For example

file m.py:

def a(s):
    exec('print '+s)

main code:

import m
x=2
m.a('x*2')

Answer 1

You want to use eval() here and not exec().

But what are you actually trying to do....the usage of eval() and exec() is in general bad style and in general not needed (especially scary when it comes to security considerations).

Answer 2

You can hack it by directly importing the special __main__ module. In m.py :

def print_global(name):
  import __main__
  print getattr(__main__, name)

And in the main module:

import m
x = 2
m.print_global('x')  # prints 2

While this example illustrates how to programatically work with the namespace, this is the kind of thing that should be done sparingly if at all.

Answer 3

Why can't you just use (okay, if you seriously do have strings somehow, but then since it's almost all in code anyway, it just looks like you've got strings around it for some reason)

(re-written code):

file m.py:

def a(s):
    print s

main code:

import m
x=2
m.a(x * 2)