FAQ 1.7.3 : How can I have modules that mutually import each other

[MackS]

Hi

I'm new to Python, I've read the FAQ but still can't get the following
simple example working:

# file main_mod.py:

global_string = 'abc'

def main():

    import auxiliary_mod
    instance = auxiliary_mod.ClassA()
    instance.fun()
    return

main()

# file auxiliary_mod.py:

class ClassA:

  def fun(self):

    import main_mod

    print 'this is ClassA.fun() and global_string is ' +
main_mod.global_string

    return

In words, the problem is: I've a main module which defines a global
variable and instantiates a class defined in a second module, and a
method of that class needs to access the global variable defined in the
main module.

When I run main_mod.py the method is executed twice:

this is ClassA.fun() and global_string is abc
this is ClassA.fun() and global_string is abc

How can I avoid this problem even in this simple example? If I move the
import main_mod statement to the outside of the definion of ClassA I
get an exception:

Traceback (most recent call last):
  File "./main_mod.py", line 4, in ?
    import auxiliary_mod
  File "/manel/ewt/test/auxiliary_mod.py", line 4, in ?
    import main_mod
  File "/manel/ewt/test/main_mod.py", line 13, in ?
    main()
  File "/manel/ewt/test/main_mod.py", line 9, in main
    instance = auxiliary_mod.ClassA()
AttributeError: 'module' object has no attribute 'ClassA'


As far as I can tell I'm following the technique suggested by Guido
himself to handle mutual imports:

"Guido van Rossum recommends avoiding all uses of from <module> import
..., and placing all code inside functions. Initializations of global
variables and class variables should use constants or built-in
functions only. This means everything from an imported module is
referenced as <module>.<name>."

[http://www.python.org/doc/faq/programming.html]

How can I get this simple example to work?

Thank you for any help in advance,

Mack