Using object of imported class as global variable of another class in Python -

I have participated in the following problem in Python. I suppose you have 3 files:

1 ) A.py (defines class A):

  class A: def a_method (self): print "global usage experiment" / code>  
 2) B.py (defines class B which uses class A's global object method):  
  class B: def b_method (self): print "a_method () Calling from ... "obj_a.a_method ()   
 3) global_ex.py:  
  import from obj_a Obj_b = B () obj_b.b_method ()   
 When I run global_ex.py, I get an error:  
  Error named: global name 'obj_a' is not defined   
 If instead of importing another b.py, I copy them into global_ex.py I work.  
 What's the problem here? Generally, what is the best way to use an object's methods in an object?  
 Thanks in advance.   
 
 
 Edit:  
 Try:  
  Import from a class B (): def __init __ (self): self.a_obj = A () DEF B_Maneth (self): Print "Calling A_the (B) B ..." self.a_obj.a_method ()   
 or:  
  square b (): def __init__ (self, a_inst): self.a_inst = a_inst def b_method (self): print "calling_a_dethod ) From B ... "self.a_inst.a_method ()