Functions – Python

If you want to reuse code, you can use a function.

This prevents you from writing the same thing over and over again.

A function has a unique distinct name in the program. Once you call a function it will execute one or more lines of codes, which we will call a code block.

Function example

For example, we could have the Pythagoras function.

In case your math is a little rusty, a^2 + b^2 = c^2. Thus, c = sqrt( a^2 + b^2). In code we could write that as:


import math

def pythagoras(a,b):
    value = math.sqrt(a *a + b*b)
    print(value)

pythagoras(3,3)

import math

def pythagoras(a,b):

value = math.sqrt(a *a + b*b)

print(value)

pythagoras(3,3)

We call the function with parameters a=3 and b =3 on the last line. A function can be called several times with varying parameters. There is no limit to the number of function calls.

Note: The def keyword tells Python we define a function. Always use four spaces to indent the code block, using another number of spaces will throw a syntax error.

Return value

It is also possible to store the output of a function in a variable. To do so, we use the keyword return.


import math

def pythagoras(a,b):
    value = math.sqrt(a*a + b*b)
    return value


result = pythagoras(3,3)
print(result)

import math

def pythagoras(a,b):

value = math.sqrt(a*a + b*b)

return value

result = pythagoras(3,3)

print(result)

The function pythagoras is called with a=3 and b=3. The program execution continues in the function pythagoras. The output of math.sqrt(a*a + b*b) is stored in the function variable value. This is returned and the output is stored in the variable result. Finally, we print variable result to the screen.

Download Exercises

6 Comments

Napoleon says:

at

When I initially commented I clicked the “Notify me when new comments are added” checkbox and now each time a comment is added I get three e-mails with the same comment. Is there any way you can remove people from that service? Cheers!

Log in to Reply
- CodeNinja says:
  
  at
  
  Removed your mail address, should be good now. Let me know if you still get mails
  
  Log in to Reply
Ayush says:

at

How do you do addition and subtraction?
By the way I am a beginner

Log in to Reply
- CodeNinja says:
  
  at
  
  def add(a,b): return a+b def sub(a,b): return a-b print( add(5,4) ) print( sub(3,2) )
  
  0
  1
  2
  3
  4
  5
  6
  7
  8
  9
  
  def add(a,b):
  return a+b
  
  def sub(a,b):
  return a-b
  
  print( add(5,4) )
  print( sub(3,2) )
  
  Log in to Reply
Sebastian says:

at

You got a small typo below the first block of code. I think it’s supposed to be ‘y=3’. 🙂

Log in to Reply
- CodeNinja says:
  
  at
  
  Thanks Sebastian!
  
  Log in to Reply

Function example

Return value

6 Comments

Leave a Reply Cancel reply