How Do I Access and Modify Global Variables in Python Functions?

Accessing and Modifying Global Variables within Functions

When working with functions in Python, one may encounter the need to access or modify variables that exist outside of the function's local scope. This is where global variables come into play.

Global variables are variables that are defined outside of all functions and are accessible throughout the program. However, when assigning a value to a global variable within a function, the global keyword must be used to indicate that the modification should be applied to the global scope rather than creating a local variable with the same name.

Declaring and Using Global Variables

To use a global variable within a function, you can declare it as such:

globvar = 0

def set_globvar_to_one():
    global globvar  # Declare this is the global variable
    globvar = 1

Here, the global keyword is used within the function to indicate that globvar should be treated as a global variable. This allows the function to modify the global variable's value.

Accessing Global Variables

To access a global variable without modifying it, the global keyword is not necessary:

def print_globvar():
    print(globvar)  # No global declaration needed for reading

Potential Pitfalls

It's important to be aware that if globvar = 1 is encountered within a function without the global keyword, Python assumes a local variable is being created, which can lead to unintended behavior. Therefore, the global keyword is essential whenever modifying global variables within functions.

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