Python – Accessing object variables within a module

I have a module (a python file, that is) containing different classes with functions, here called ‘Experiment_1’. When running it as the main file, all objects can access all variables – object_2 functions can access variables in object_1, and so on:

# Experiment_1
class A():
    def process1(self):
        self.x=10

    def process2(self):
        self.y=20

class B():
    def addition(self):
        summed=object_1.x+object_1.y
        print(summed)

if __name__ == '__main__':
    object_1=A()
    object_2=B()
    
    object_1.process1()
    object_1.process2()

    object_2.addition()

Next, I attempt to run this in file ‘Experiment_2’ as an imported module:

# Experiment_2
from Experiment_1 import *
import Experiment_1

object_1=A()
object_2=B()

object_1.process1()
object_1.process2()

object_2.addition()

And get the error message:

  File "C:\Program Files\Sublime Text 3\Experiment_2.py", line 10, in <module>
    object_2.addition()
  File "C:\Program Files\Sublime Text 3\Experiment_1.py", line 10, in addition
    summed=object_1.x+object_1.y
NameError: name 'object_1' is not defined

Thus, object_2 can no longer access the variables of object_1. I have been searching a lot to find a solution to this but may be using the wrong keywords or simply lack the understanding to recognize the answer when I see it – can anyone give me a hint how to proceed?

Thanks in advance!

>Solution :

The issue is your object instantiation in Experiment_1.py. The code inside the below block only get executed if you run the file as a script and NOT when you import it.

if __name__ == '__main__':
    pass

So in your object of class B, the below statement in addition method,

#Experiment_1.py

summed=object_1.x+object_1.y

see object_1 as not defined, because it is only instantiated in the if __name__ == '__main__': block which is not executed when importing the module.

See this question: What does if __name__ == "__main__": do?

And for the solution, If you wish to use the module structure, the work around is to pass the object to the addition method.

#Experiment_1.py
class A():
    def process1(self):
        self.x = 10

    def process2(self):
        self.y = 20


class B():
    def addition(self, obj):
        summed = obj.x + obj.y
        print(summed)

then in your next file,

from Experiment1 import *
# import Experiment1

object_1=A()
object_2=B()

object_1.process1()
object_1.process2()

object_2.addition(object_1)