Functions

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

We can control the flow of a program by calling a function. If we call a function, it executes, returns a value, and then resumes the program where it was called.

In programming, a named section of a program that performs a specific task is called a function. 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. Please watch the video below and remember the content.

The difference between returning and printing

Students often print from within a function. Please understand the difference between printing a result from a function and returning a result from a function.

print: gives the value to the user as an output string. print(3) would give a string '3' to the screen for the user to view. The program would lose the value.

return: gives the value to the program. Callers of the function then have the actual data and data type (bool, int, etc...) return 3 would have the value 3 put in place of where the function was called.

In general, you should return a value from a function and not directly print from a function.

Example of a function

#
# this is a simple function that remembers who like hamburgers and who doesn't like hamburgers. 
#

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

See Also

• Lambda functions