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Unlocking the Power of Global Variables in Python

The Basics of Variable Scope

Before diving into the world of global variables, it’s essential to understand the fundamentals of Python variable scope. In Python, a variable’s scope determines its visibility and accessibility within a program. A solid grasp of variable scope will help you master the art of working with global variables.

Accessing Global Variables from Within Functions

Imagine you have a global variable, and you want to access it from inside a function. This is where things get interesting. You can easily access a global variable from within a function, but what happens when you try to modify it? Let’s take a look:


c = 1
def add():
print(c)
add() # Output: 1


As you can see, we’ve successfully accessed the global variable c from within the add() function. However, if we try to modify c from inside the function, we’ll run into trouble:


c = 1
def add():
c = c + 2
print(c)
add() # Output: Error!


The reason for this error is that Python treats c as a local variable by default, and we can’t modify a global variable from within a function without explicitly declaring it as global.

The Solution: Using the Global Keyword

This is where the global keyword comes to the rescue. By using global, we can modify a global variable from within a function. Let’s see how:


c = 1
def add():
global c
c = c + 2
print(c)
add() # Output: 3


As you can see, we’ve successfully modified the global variable c from within the add() function using the global keyword.

The Rules of the Global Keyword

Now that we’ve seen the power of the global keyword, let’s explore its rules:

• Local by Default: When you create a variable inside a function, it’s local by default.
• Global by Default: When you define a variable outside of a function, it’s global by default – no need to use the global keyword.
• Modify with Care: Use the global keyword to modify a global variable inside a function.
• No Effect Outside: Using the global keyword outside a function has no effect.

Working with Nested Functions

But what happens when we have nested functions? How do we access and modify global variables in such scenarios? Stay tuned for our next article, where we’ll explore the intricacies of global variables in nested functions.

Further Reading

• Python Variables, Constants, and Literals: Dive deeper into the world of Python variables.
• Python globals(): Learn about the globals() function and its role in working with global variables.