Functions allow us to reuse bits of code. For example, say that we are calculating tax on transactions. We can wrap up our code in a functional unit and give it a name:

def calculate_tax(price, tax):
    sales_tax = price * tax
    total = price + sales_ tax
    return total

From then on we can just call that name and pass it some information (called parameters or arguments):

calculate_tax(53.79, 0.075)

This will save us time as well as make our code easier to review. Lets take a look at some more in-depth learning resources.

Learning Resources

Python for Informatics

• Chapter 4 - Functions (Slides, Printable Slides, Streaming Video, Download Video, Lecture Audio)
• Worked Exercise Screencasts: 4.4 (suggest download)

Dive Into Python3:

• Ch 1.2 Declaring Functions

Practice

Post chapter excercises and questions below.

Q:  What is an example of a machine or process that takes external input and returns a modified output?

Q: How many tasks do you think that an individual function should generally perform?