Why reset python global value doesn't take effect

Question

Just confused about global value in Python, here are two piece of code

#gl.py

import cli

a = 1    
print "gl 1: %d %d" % (id(a), a)


def reset():
    global a
    a = 7
    print "reset 1: %d %d" % (id(a), a)


if __name__ == '__main__':
    cli.handler(reset)
    print "gl 2: %d %d" % (id(a), a)

the cli code

#cli.py

def handler(func):
    from gl import a
    print "cli 1: %d %d" % (id(a), a)
    func()
    print "cli 2: %d %d" % (id(a), a)

The result of execution is

$ python gl.py
gl 1: 150847672 1
gl 1: 150847672 1
cli 1: 150847672 1
reset 1: 150847600 7
cli 2: 150847672 1    #Why value doesn't change
gl 2: 150847600 7

Here I don't understand after "function reset()" execution, the result of global value doesn't change in cli.py(cli 2: 150847672 1), but back to gl.py, global value does change!!

Answer 1

Two concepts are missing here

• Globals are globals to modules and not across modules

Refer: http://legacy.python.org/doc/essays/ppt/hp-training/sld036.htm

Refer: http://docs.python.org/release/2.4/ref/global.html

• Variables are imported as Values and not by reference

Refer: https://stackoverflow.com/a/3338357/977038

If you need to share Global variables across modules refer How do I share global variables across modules?

Answer 2

Your gl module is imported twice into two different namespaces

try this:

import sys
print sys.modules['__main__'].a
print sys.modules['gl'].a