Functions in Python

A function is a block of code which only runs when it is called.

You can pass data, known as parameters, into a function.

A function can return data as a result.

Creating a Function

In Python a function is defined using the def keyword:

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

Calling a Function

To call a function, use the function name followed by parenthesis:

my_function()
Hello from a function

Arguments

Information can be passed into functions as arguments.

Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just separate them with a comma.

def my_function(input_sample):
  print(input_sample + " Office")
my_function("Big")
my_function("Small")

Big Office
Small Office

The terms parameter and argument can be used for the same thing: information that are passed into a function.

Number of Arguments

By default, a function must be called with the correct number of arguments. Meaning that if your function expects 2 arguments, you have to call the function with 2 arguments, not more, and not less.

def my_function(input_1,input_2):
  print(input_1 + " " + input_2)

my_function("Big", "Office")

Big Office

Arbitrary Arguments, *args

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

def my_function(*kids):
  print("The youngest child is " + kids[2])

my_function("Ahmed", "Ali", "Manar")
The youngest child is Manar

Keyword Arguments

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

This way the order of the arguments does not matter

def my_function(child3, child2, child1):
  print("The youngest child is " + child3)

my_function(child1 = "Ahmed", child2 = "Ali", child3 = "Manar")
The youngest child is Manar

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.

def my_function(**kid):
  print("His last name is " + kid["lname"])

my_function(fname = "Mohamed", lname = "Ali")
His last name is Ali

Default Parameter Value

The following example shows how to use a default parameter 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("Sweden")
my_function("India")
my_function()
my_function("Brazil")

I am from Sweden
I am from India
I am from Norway
I am from Brazil

Passing a List as an Argument

You can send any data types of argument to a function (string, number, list, dictionary etc.), and it will be treated as the same data type inside the function.

def my_function(food):
  for x in food:
    print(x)

fruits = ["apple", "banana", "cherry"]

my_function(fruits)
apple
banana
cherry

Return Values

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

def my_function(input_sample):
  return 10*input_sample

print(my_function(2))
print(my_function(7))
print(my_function(5))
20
70
50

The pass Statement

function definitions cannot be empty, but if you for some reason have a function definition with no content, put in the pass statement to avoid getting an error.

def myfunction():
  pass
  

You can refer to the code from here