In the context of our previous discussion, defining a function is the process of creating a new function in your code. You are essentially teaching the computer a new command that it can execute later.

This is done using the def keyword. The definition includes the function's name, the parameters it accepts, and the block of code it will run when called.

The Syntax of a Function Definition

A function definition has several key parts:

1.   def keyword: This tells Python that you are about to define a function.

2.   Function Name: You choose a name for your function (e.g., greet, calculate_area). It should be descriptive and follow Python's naming conventions (usually snake_case).

3.   Parentheses (): These are required after the function name. They hold the list of parameters the function will accept.

4.   Colon :: This marks the end of the function's header and the beginning of its body.

5.   Indented Code Block: The lines of code that make up the function's body must be indented. This is how Python knows which instructions belong to the function.

Example

Here is the code from our previous discussion that defines a function named calculate_area.

Python

# This entire block is the function definition.

def calculate_area(length, width):

    """

    This is a docstring explaining the function.

    """

    area = length * width

    return area

When Python runs this def block, it doesn't execute the code inside it. Instead, it creates a new function object and assigns it to the name calculate_area. The code inside is only executed later when you call the function, like this:

Python

rectangle_area = calculate_area(10, 5)

Think of it like writing down a recipe. The def block is the recipe itself (the definition). Calling the function (calculate_area(10, 5)) is like actually following the recipe to cook the dish.