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

Question

I have run into the following issue in Python. Suppose you have 3 files:

1) a.py (defines class A):

class A:
  def a_method(self):
    print "global var experiment"

2) b.py (defines class B that uses method of the global object of class A):

class B:
  def b_method(self):
    print "calling a_method() from B..."
      obj_a.a_method()

3) global_ex.py:

from a import A

obj_a=A()       
obj_a.a_method()

from b import B

obj_b = B()
obj_b.b_method()

When I run global_ex.py I get the error:

NameError: global name 'obj_a' is not defined

If instead of importing a.py and b.py I copy-paste them into the global_ex.py it works fine.

What is the issue here? Generally, What is the best way to use methods of one object in another object?

Thank you in advance.

well, obj_a is not defined in the global scope of b.py - would you like the interpreter to copy-paste the text of the imported module instead of using compiled bytecode? — Aprillion
– Aprillion, Commented Mar 28, 2013 at 0:14

Artsiom Rudzenka · Accepted Answer · 2013-03-27 23:55:29Z

1

EDITED:

Try:

from a import A

class B():

  def __init__(self):
      self.a_obj = A()

  def b_method(self):
      print "calling a_method() from B..."
      self.a_obj.a_method()

Or:

class B():

  def __init__(self, a_inst):
      self.a_inst = a_inst

  def b_method(self):
      print "calling a_method() from B..."
      self.a_inst.a_method()

edited Mar 27, 2013 at 23:55

answered Mar 27, 2013 at 7:17

Artsiom Rudzenka

29.3k5 gold badges36 silver badges53 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

jazzblue Over a year ago

Thanks, however, I gave a simple example here. In my real case class A contains other members and methods which should be accessible by other classes. Right now I am thinking that maybe the best way would be to pass obj_A as and argument to b_method. It should work that way, shouldn't it?

Artsiom Rudzenka Over a year ago

@GregoryR - yes, it would work the way you mentioned and it one of the use-cases

martineau Over a year ago

@GregoryR: Instead of passing obj_a to b_method() every time you call it, you could also add an __init__() method to class B and pass obj_a to it just once when you construct obj_b -- of course __init__() would have to save the value for access later in b_method as needed something like what is shown in the second example of this answer.

jazzblue Over a year ago

@martineau: Thanks. When I pass obj_a to __init__() of class B, is it passed by reference? (In other words, if obj_a gets updated, will class B be aware of these updates?)

martineau Over a year ago

@GregoryR: Yes, since it's an instance of a mutable class.

|

Collectives™ on Stack Overflow

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

1 Answer 1

8 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

8 Comments

Your Answer

Sign up or log in

Post as a guest

Related