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Python Functions

3 min read ·

A function is a block of reusable code that performs a specific task. Functions help in:
  • Reducing code repetition
  • Improving readability
  • Making programs modular and organized
Once a function is defined, it can be called multiple times.

Why Use Functions?

Functions are used to:
  • Break large programs into smaller parts
  • Reuse logic instead of rewriting code
  • Make debugging and maintenance easier

Syntax of a Function

  • def is a keyword used to define a function
  • function_name follows variable naming rules
  • Parentheses () are mandatory
  • Function body must be indented

Simple Function Example

Calling the function:

Function with Parameters

Parameters allow passing data to a function.
Calling the function:

Function with Multiple Parameters

Function with Return Statement

The return statement sends a value back to the caller.
Note

A function stops executing once return is encountered.

Function Without Return (Void Function)

Default Parameter Values

Keyword Arguments

Positional Arguments

Function with *args

Used to pass multiple arguments.

Function with **kwargs

Used to pass key-value pairs.

Calling a Function Inside Another Function

Nested Functions

Function with Conditional Logic

Function with Loop

Scope of Variables in Functions

  • Variables inside a function are local
  • They cannot be accessed outside

Common Mistakes with Functions

Forgetting to Call the Function ❌

Function will not run until called.

Missing Parentheses ❌

Caution

Always use () while calling a function.

Real World Example

Real World Scenario

ATM balance check using function

Exercise

Practice Task
  1. Create a function to add two numbers
  2. Write a function to check prime number
  3. Create a function that returns square of a number
  4. Use *args to calculate sum of numbers
  5. Create a function to display user details