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

Answer 1

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

Answer 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.

• user395760: "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.