How Can I Effectively Share Global Variables Between Multiple Python Files?

Sharing Global Variables Between Files

In software development, defining global variables across multiple files can present certain complexities. To address this challenge, it's important to understand the concept and limitations of global variables.

Global variables are variables declared outside the scope of any function or class, typically at the module level. They are accessible from anywhere within the module. However, this can lead to potential issues when sharing global variables between multiple files.

Consider the following example:

# main.py
global myList
myList = []
import subfile
subfile.stuff()
print(myList[0])

# subfile.py
def stuff():
    globals()["myList"].append("hey")

This code attempts to use a global variable myList defined in main.py within subfile.py. However, this approach fails because subfile.py has no knowledge of myList. To resolve this, we need an alternative approach.

In Python, a cleaner solution is to centralize global variables in a separate module:

# settings.py
def init():
    global myList
    myList = []

Next, import and initialize the global variable from other files:

# subfile.py
import settings
def stuff():
    settings.myList.append('hey')

# main.py
import settings
settings.init()          # Initialize global var once
subfile.stuff()         # Do stuff with global var
print settings.myList[0] # Check the result

By isolating global variable definition and initialization in settings.py, we ensure that the global variable is only initialized once and accessible from all other modules. This approach provides a structured and maintainable way to share global variables across multiple files.

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