模块内的 python 全局变量

Question

a.py contains:

ip=raw_input()
import b
show()

b.py contains:

def show:
    global ip
    print ip

it's showing an error saying that ip is not defined. how can i use a variable from the main script inside a module?

Answer 1

A global declaration prevents a local variable being created by an assignment . It doesn't magically search for a variable.

Unless you import a variable from one module to another, it is not available in other modules.

For b to be able to access members of a , you would need to import a . You can't, because a imports b .

The solution here is probably just not to use global variables at all.

Answer 2

The way your code is structured, it implies to me that you're treating import as if it were effectively copying-and-pasting the contents of b.py into a.py . However, that's not how Python works -- variables and functions inside one module will not be accessible in another unless explicitly passed in via a function, or by using the module.member notation.

Try doing this instead:

a.py:

import b

ip = raw_input()
b.show(ip)

b.py:

def show(ip):
    print ip

If you need to do some processing within the b module, pass in the relevant functions, make any changes, and return them. Then, reassign them within the calling module.

Edit: if you must use globals, change b.py to look like this:

ip = None

def show(temp):
    global ip
    ip = temp

    # code here

    print ip

...but it would be more ideal to restructure so that you don't end up using globals.

Answer 3

i moved some of the code of a.py to b.py like raw_input() and then the b.py just returns what is being needed in a.py .

so no need to worry about global variables etc. as half of the work is being done by b.py .