04 Python Functions

A function is organized, reusable code that is used to perform a single or related action. Python has lots of built in function, but one can also create their own functions. These are called user-defined functions.

Defining a Function:

Function blocks begin with the keyword "def" followed by the function Name and parentheses ( ).
Any input parameters or arguments should be placed within these parentheses. You can also define parameters inside these parentheses. The code block within every function starts with a colon (:)

Example 01: 

Here, we have defined a Happy Birthday Function.

def happyBirthday(name):

    print("Happy Birthday to you!")
    print("Happy Birthday to you!")
    print("Happy Birthday, dear, " + name + "!")
    print("Happy Birthday to you!\n")

happyBirthday('Jyoti')

and you will see following output.

Example 02: 

Same Happy Birthday Function, however, input from user

def happyBirthday(name):

    print("Happy Birthday to you!")
    print("Happy Birthday to you!")
    print("Happy Birthday, dear, " + name + "!")
    print("Happy Birthday to you!\n")

def main():
    userName = input("Enter the Birthday person's Name: ")   
    happyBirthday(userName)

main()

and you will see following output.

Example 03: 

Function with more than one input parameter.  Here function sumfunc add two input value, which is called from main function.

def sumfunc(x, y):
      sum = x + y
      sentence = 'The sum of {} and {} is {}.'.format(x, y, sum)   # Remember, no comma
      print(sentence)

def main():

    a = int(input("Enter an integer: "))
    b = int(input("Enter another integer: "))
    sumfunc(a, b)

main()

and you will see following output.

this same code can be written in a slight different way,

def sumfunc(x, y):
      sum = x + y
      return sum

def main():

    a = int(input("Enter an integer: "))
    b = int(input("Enter another integer: "))
    c = sumfunc(a, b)
    print("The sum is:", c)

main()

Example 04: 

Here, function with global constant are shown. We defined PI as a global constant and calculated the Circle Area and Circumference.

PI=3.14159                                   # defining global constant

def circleArea(radius):
return PI*radius*radius      #  Circle Area = PI*r^2

def circleCircumference(radius):
return 2*PI*radius

def main():
r=int(input("Enter tha Radius of the circle in meter:"))     # you may use float
cA=circleArea(r)
cC=circleCircumference(r)
print("Circle Area: {} m^2".format(cA)) # Remember, no comma
print("Circle Circumference: {} m ".format(cC))

main()

and you will see following output.