Functions

A function is a block of reusable code that performs a specific task.

Functions help in organizing code, making it easier to maintain. They allow you to break down a complex problem into smaller, more manageable tasks, and you can call these functions whenever you need to execute the associated code.

Types of Functions

There are two types of functions:

Built-in functions: Predefined in Python, such as len(), max(), print(), sum(), etc.
User-defined functions: Functions created by the user to perform custom tasks.

Creating a Function

The def keyword is used to define a function in Python.

Syntax:

def function_name(parameters):
  # Code block

For example:

def greet():
    print("Hello!")

Calling a Function

You can call a function by giving the function name, followed by parameters (if any) in the parenthesis.

For example:

def add(a, b):
  print(a + b)
 
add(5, 3) #output: 8

If you want to declare a function and don’t want to give any code statements at that time, then you can use the pass statement to avoid any errors.

For example:

def add(a, b): #This gives a syntax error

You can use the pass statement to avoid this as follows:

def add(a, b):
  pass

Function Arguments

Functions can accept inputs, called arguments. There are four types of arguments that you can provide in a function:

Default Arguments
Keyword Arguments
Required Arguments
Variable length Arguments

Default arguments

You can provide a default value for parameters while creating a function. This way if you don’t provide any value at the time of function call then the function will take the default values.

For example:

def greet(name="Mark"):
  print("Hello", name)
 
greet("John") # output: Hello John
greet() # output: Hello Mark

Keyword arguments

You can provide arguments in key = value syntax. This way, the interpreter identifies the arguments based on their parameter names, so the order in which the arguments are passed becomes unimportant.

For example:

def greet(firstName, lastName):
  print("Hello", firstName, lastName)
 
greet(lastName = "Phillips", firstName="Mark") 
# output: Hello Mark Phillips

Required arguments

In case you don’t pass the arguments with a key = value syntax, then it is necessary to pass the arguments in the correct positional order and the number of arguments passed should match with actual function definition.

For example:

def greet(firstName, lastName):
  print("Hello", firstName, lastName)
 
greet("Mark", "Phillips") # output: Hello Mark Phillips

Variable-length arguments

Sometimes you may need to pass more arguments than those defined in the actual function. This can be done using variable-length arguments.

You can achieve this in the following two ways:

Arbitrary Arguments:

While creating a function, pass a * (args) before the parameter name. The function accesses the arguments by processing them in the form of tuple.

For example:

def greet(*names):
    print("Hello,", names[0], names[1])
 
greet("Mark", "John")
#output: Hello, Mark John

Keyword Arbitrary Arguments:

While creating a function, pass a ** (kwargs) before the parameter name. The function accesses the arguments by processing them in the form of dictionary.

def greet(**names):
    print("Hello,", names["firstName"], names["lastName"])
 
greet(firstName = "John", lastName = "Doe")
#output: Hello, John Doe

Return Statement

The return statement is used to return a value back to the caller.

For example:

def add(a, b):
  return a + b
  
result = add(5, 3)
print(result)  # Output: 8

Why Use Functions?

Functions avoid rewriting the same code and makes your code reusable.
Break large programs into smaller, manageable pieces.
Functions clearly define their purpose, so it improves readability.
Debug and update specific parts without affecting the rest.