Functions in Python

A function f takes an input x, and returns a single output f(x). One metaphor describes the function as a "machine" or "black box" that for each input returns a corresponding output.

Introduction

In programming, a named section of a program that performs a specific task. In this sense, a function is a type of procedure or routine. Some programming languages make a distinction between a function, which returns a value, and a procedure, which performs some operation but does not return a value.

Most programming languages come with a prewritten set of functions that are kept in a library. You can also write your own functions to perform specialized tasks.

We use function so we don't need to repeat ourselves.

Example of a function

#
# this is a simple function
#

def welcome(name):
    if name == "Alisher":
        likes_hamburgers ="yes"
    else:
        likes_hamburgers="no"
    return likes_hamburgers
    
print welcome("Bill")
print welcome("Alisher")    
print welcome("foo")

Another classic example of a function

#
# this is a simple function
#

def calculator(number1, number2):
    answer = number1 + number2
    return answer
    
print calculator(12,43)
print calculator(91,673)
print calculator(1,3)
print calculator(87,1098)

Some decent videos about functions in Python

In the video below, the programmer uses a different IDE than we do (we use canopy). The programmer also uses tests in this video, which we haven't covered yet.