a.py

print "module A being imported!"

def holler():
  print "hollering from A"

import b
b.pull_from_a()

b.py

print "module B being imported!"

def pull_from_a():
  import a
  a.holler()

OUTPUT

[shuchen@archy stuff]$ python2.7 a.py 
module A being imported!                                                                                  
module B being imported!                                                                                  
module A being imported!                                                                                  
hollering from A                                                                                          
hollering from A