Python Functions

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.

In Python a function is defined using the def keyword

def welcome():
  print('Welcome to All')

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

welcome()

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.

The following example has a function with one argument (name). When the function is called, we pass along a first name, which is used inside the function to print the name.

def print_name(name):
  print(name)
 # calling function
 print_name('Ahmed')
 print_name('Abdelrhman')

# define function has more than one argument
 def print_full_name(fname,lname):
  print(fname+' '+lname)
 # calling function
 print_full_name('Ahmed','Mohamed')
 print_full_name('Abdelrhman','Gaber')

The following example shows how to use a default parameter value.

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

# if we didn`t pass any value it will take the default
 def add(x , y=3):
  z = x + y
  print('Result = '+str(z))
 # calling function
 add(7) # there is no error because it takes the default value of y = 3 so the result is 10
 add(7,7)

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

# get the power 2 of any passing value in the list
 def power_2(l):
  return [i**2 for i in l]
 

# calling function and pass a list of numbers it will return a list of power two for each number
 power_2([1,2,3,4,5,6])

functions make our code more readable and efficient and save time and call it when we need.