How to use a global variable in a function in Python?

Elevating Code Clarity: Properly Managing Global Variables in Python

Relying on global variables in Python can be a contentious topic. On one hand, global variables allow you to share state across multiple functions without extensive parameter passing. On the other, overuse can lead to tangled code that’s harder to maintain. When you need to use a global variable inside a function—perhaps for a configuration setting or a shared resource handle—Python makes it possible with a special keyword: global.

By default, variables defined outside a function’s scope are accessible inside that function, but only in a read-only manner. Attempting to assign a new value to such a variable within the function’s body will create a local variable with the same name, leaving the global variable untouched. The global keyword provides a way around this limitation. Declaring a variable as global within the function signals to Python that assignments to this variable refer to the one defined at the module level.

A Simple Example
Imagine you have a global counter that needs to be updated by multiple functions:

counter = 0  # This variable is defined in the global scope

def increment_counter():
    global counter  # Tell Python we mean the global 'counter'
    counter += 1     # Now we're incrementing the global variable

increment_counter()
increment_counter()
print(counter)  # Output: 2

Without the global keyword, the assignment counter += 1 inside increment_counter() would create a local counter, leaving the global version unchanged.

When to Use Global Variables

• Configuration Settings: Perhaps your application relies on a configuration value that must be accessible and modifiable throughout multiple parts of the program. A global variable can store this configuration, allowing functions to adjust or read the setting without passing it around.
• Shared Resources: If you manage a connection or resource pool at a module level, functions can reference and update it globally. Still, this should be approached cautiously and documented well.

Cautions and Best Practices

1. Minimize Global State: Over-dependence on global variables can make your code harder to understand and test. Because global variables can be changed by any function, it becomes harder to track when and why the state changes.

2. Use Clear Naming Conventions: When you do rely on globals, choose names that reflect their role. This makes it easier for other developers (and your future self) to understand the variable’s purpose.

3. Prefer Passing Parameters: Often, it’s more transparent to pass values into functions rather than relying on global variables. This approach keeps functions more modular and predictable.

4. Leverage Classes and Objects: Instead of relying on global variables to store state, consider using classes or singletons. Encapsulating state in objects provides a cleaner API, making it easier to reason about data flow.

Building a Strong Python Foundation
Understanding how to manage global variables, along with knowing when and when not to use them, is part of growing into a more mature Python developer. To solidify your fundamentals and gain confidence in coding best practices:

• Grokking Python Fundamentals: Ideal for beginners and those refreshing their Python basics, this course empowers you to write clean, maintainable code from the start.

If you’re preparing for coding interviews and want to sharpen problem-solving skills related to Python and general coding patterns:

• Grokking the Coding Interview: Patterns for Coding Questions: Master common coding patterns, helping you solve problems efficiently during interviews.
• Grokking Data Structures & Algorithms for Coding Interviews: Deepen your algorithmic thinking, which translates into more robust and scalable code.

Also, the DesignGurus.io YouTube channel offers valuable video content—covering coding best practices, system design insights, and interview preparation tips—making it a great complementary resource to your study materials.

Refining Your Code Quality
Global variables are a double-edged sword: convenient but potentially leading to complexity if misused. By understanding how to properly declare and manage them in Python, you remain in control. As your skills advance, you’ll know when using a global variable is a strategic choice—and when it’s time to consider more modular, object-oriented designs. With continuous learning and practice, you’ll develop an intuitive sense of when to rely on global state and when to favor other programming constructs for clearer, more maintainable code.