How to Establish Cross-Module Variable Accessibility in Python: Sharing Variables Without Sharing Instances?

Establishing Cross-Module Variable Accessibility

In Python, a convenient cross-module variable is __debug__. However, creating a custom variable with similar functionality may seem challenging. This article delves into this topic, exploring a method to define a shared variable across modules while preserving its immutability.

Solution: Leveraging Global Module-Level Variables

To establish a cross-module variable without sharing a common variable instance, consider employing global module-level variables. These variables are defined and assigned within a module and become accessible to other modules that import it. By assigning the variable before importing dependent modules, a consistent value can be established throughout the project.

An example is provided below:

a.py:

var = 1

b.py:

import a
print(a.var)
import c
print(a.var)

c.py:

import a
a.var = 2

Test:

$ python b.py
# Output
1
2

In this example, variable var is defined in module a.py and becomes accessible to module b.py upon its import. Even though module c.py changes the value of var, module b.py retains its original value.

Real-World Application

Django provides a practical use case for shared module-level variables. Its global_settings.py module serves as an example where settings are exposed as module attributes rather than a single shared object.

By employing this technique, cross-module variable sharing can be achieved while maintaining variable integrity and simplifying module code organization.

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