Python - Scope

The scope of a variable is the part of a program where that variable can be accessed.

Every variable in Python is created in a particular scope. Some variables are available throughout the module, while others are available only inside a single function.

Understanding scope is important because it decides exactly where a name is visible in our code.

Before discussing variables, it is helpful to understand the relationship between these three terms.

The relationship can be understood with the following hierarchy:

Library
├── Module 1
│   ├── Function 1
│   ├── Function 2
│   └── Function 3
└── Module 2
    ├── Function 1
    ├── Function 2
    └── Function 3

Python supports 2 types of variables based on scope:

• Global Variables
• Local Variables

The variables which are declared outside of a function are called global variables.

These variables can be accessed in all functions of that module.

The variable a is declared at module level, outside any function, so it is a global variable.

Both f1() and f2() can access a, because global variables are visible inside every function of the module.

The variables which are declared inside a function are called local variables.

Local variables are available only for the function in which we declared them. From outside the function, they cannot be accessed.

The variable a is declared inside f1(), so it is a local variable of f1().

Inside f1(), printing a works normally. But inside f2(), the name a is not in scope, so Python raises a NameError.

• It prevents variables from one function accidentally changing variables in another function.
• It allows the same variable name to be reused safely in different functions.
• It keeps the module organized because the visibility of every name is clear.
• It avoids name conflicts between different parts of a program.