when is a != foo.a?

[Chaz Ginger]

I am somewhat new to Python (last year). As such I encounter little 
"gotchas" all the time. I am wondering is someone can explain this to me:

If have three simple files:

a.py ---------------------

foo = None
def a(b):
	global foo
	foo = b

b.py ----------------------

from a import foo
def b(): print foo

c.py ----------------------

import a
from b import b

print 'per a.a() ',a.foo
a.a(245)
print 'expect 245 ', a.foo
b()


If I run 'python c.py' I get the following printed out:


per a.a()  None
expect 245  245
None


That surprised me. If I change b.py to

import a
def b(): print a.foo

I get the following (which is what I expected originally):


per a.a()  None
expect 245  245
245


Can someone explain what is really going on here?

TIA,
Chaz