18. Introduction to Python Functions

Quiz: 0/5

Functions are like mini-programs within your program. They allow you to write a block of code once and use it multiple times by calling the function's name. Functions can also take inputs (arguments) and return outputs.

Why use Functions?

• Code Reusability: Write once, use it anywhere.
• Organization: Break large programs into smaller, more manageable pieces.
• Readability: Makes your code easier to read and understand.
• Debugging: Easier to test and debug specific parts of your code.

Defining a Function in Python

To define a function, use the def keyword followed by the function name and parentheses.
Here’s the syntax:

def function_name(parameters):
    # Code block
    return value

Example: A simple Function

Let’s create a function that greets someone:

def greet():
    print("Hello! Welcome to Python programming.")

• def: Defines the function.
• greet: Name of the function.
• print("..."): Code inside the function.

You can call this function like so:

greet()
# Output: Hello! Welcome to Python programming.

Adding parameters

Parameters allow you to pass information to functions. For example:

def greet_person(name):
    print(f"Hello, {name}! Welcome to Python programming.")

Now, you can call it with different names:

greet_person("Alice")
# Output: Hello, Alice! Welcome to Python programming.

greet_person("Bob")
# Output: Hello, Bob! Welcome to Python programming.

Using return to get outputs

Functions can return values to the code that called them:

def add_numbers(a, b):
    return a + b

Call the function and store the result:

result = add_numbers(3, 5)
print(result)
# Output: 8

Scope: where variables live

• Local Variables: Exist only inside the function.
• Global Variables: Exist everywhere in your program.

Example:

x = 10  # Global variable

def multiply_by_two():
    x = 5  # Local variable
    return x * 2

print(multiply_by_two())  # Output: 10
print(x)  # Output: 10 (global x is unchanged)

Conclusion

Functions are powerful tools that make your code more efficient and easier to manage. By learning to define and use them, you’re taking a significant step toward writing better programs!