Python scope / namespace issue

Question

I have two python modules:

//// funcs.py

from classes import *

def func():
    d = D()
    print "func"

if __name__ == "__main__":
    c = C()

//// classes.py

from funcs import *

class C:
    def __init__(self):
        print "C class"
        func()

class D:
    def __init__(self):
        print "D class"

Running funcs.py yields a NameError saying that "global name 'D' is not defined". However if I comment out the creation of the D() instance, everything works fine.

Why does this happen?

Thanks

Gandi · Accepted Answer · 2011-08-29 10:13:26Z

5

This one works fine without complicating your code:

///funcs.py

import classes

def func():
    d = classes.D()
    print "func"

if __name__ == "__main__":
    c = classes.C()

///classes.py

import funcs

class C:
    def __init__(self):
        print "C class"
        funcs.func()

class D:
    def __init__(self):
        print "D class"

Sometimes it's much better to use simple import, than from ... import .... There is quite good article on that: http://effbot.org/zone/import-confusion.htm

answered Aug 29, 2011 at 10:13

Gandi

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Comments

Vijay Varadan · Accepted Answer · 2011-08-29 10:12:23Z

2

The problem occurs due to the attempt to use a cyclically imported module during module initialization. To clarify, using the "from module use *" requires that a module be compiled. Instead if you switch to using "import module" in both cases, it should work fine.

answered Aug 29, 2011 at 10:12

Vijay Varadan

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1 Comment

user395760 Over a year ago

"requires that a module be compiled" is misleading at best. The module code is loaded, compiled and run either way. But from m import * copies everything that's in the module at that point in time while import m gives a reference to the module object - and hence makes later modifications visible.

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