Trying to access a global variable from class instance in Python

Question

I am trying to access a global variable which was defined in my main Python file from inside an object instance. I have read some other questions on the topic and I learned I need to use the global keyword inside my class method first.

However, even so, my code does not seem to work:

from secondclass import SecondClass

somelist = [1,2,3]
obj = SecondClass()

obj.mainmethod()

And here is my other file containing secondclass:

class SecondClass():
  
  def mainmethod(self):
    global somelist
    print (somelist)

Even through I am using the global keyword, Python still gives me error:

NameError: name 'somelist' is not defined

Why is that?

In Python, global is local to the module. It is not global worldwide. If your class needs that list, then you should pass it to the constructor. — Tim Roberts
– Tim Roberts, Commented Apr 27, 2022 at 5:53

Bharel · Accepted Answer · 2022-04-27 06:12:47Z

2

global is scoped to the same module.

You have multiple options to solve this, among them:

Pass the variable to the class and use self.attribute.
Pass the variable to the method.
Create a module holding the global, such as globals.py and import it from both sides.
Inject the global using import secondclass; secondclass.somelist = [1,2,3]

And plenty of other solutions.

Personally, I'd go for the first or second any day of the week.

edited Apr 27, 2022 at 6:12

answered Apr 27, 2022 at 5:56

Bharel

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