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Python Functions

Overview

A function in Python is a block of code that only runs when it is called. Functions are useful for reducing code complexity and repetition.

Example of a Simple Function

def function_name(): print("Hello from a function")

In this example, function_name() is a function that prints a message when it is called.

Benefits of Using Functions

  • Reduces Complexity: Functions allow you to break down your code into smaller, more manageable pieces.
  • Reduces Repetition: Functions can be reused multiple times throughout your code, reducing the need to write the same code over and over again.

Variable Classification in Functions

Variables used in functions can be classified into two categories:

Global Variables

  • Definition: A global variable is a variable that is declared outside of any function. It can be accessed from anywhere in the program.

  • Example:

    global_var = "I am global"

    def print_global(): print(global_var)

    print_global() # Output: I am global

Local Variables

  • Definition: A local variable is a variable that is declared inside a function. It can only be accessed within that function.

  • Example:

    def print_local(): local_var = "I am local" print(local_var)

    print_local() # Output: I am local

Reference Code

Arguments

Values can be passed into functions as arguments.

Positional Arguments

You can specify that a function can have ONLY positional arguments, or ONLY keyword arguments.

def add(a, b):
    print(a + b)

add(1,2)

Reference Code

Arbitrary Arguments

Many arguments that will be passed into your function. add a * before the parameter name in the function definition.
This way the function will receive a tuple of arguments, and can access the items accordingly:

def num(*a):
    print(a)

num(1,2,3,4,5,a,b)

Default Arguments Value

If we call the function without argument, it uses the default value

def my_function(country = "Norway"):
  print("I am from " + country)

my_function()
my_function("India")

Keyword Arguments

You can also send arguments with the key = value syntax.

def add(a, b):
    print(a + b)

add(a=1, b=2) # This way the order of the arguments does not matter.

Arbitrary Keyword Arguments, **kwargs

If you do not know how many keyword arguments that will be passed into your function, add two asterisk: ** before the parameter name in the function definition.

This way the function will receive a dictionary of arguments, and can access the items accordingly:

def person(**data):
    print(data)

person(fname = "Manu ", lname = "Mathew")

Return Values

To let a function return a value, use the return statement

def my_function(x):
  return 5 * x

print(my_function(3))