Chapter 5. Functions

Up until this point, any time you wanted to accomplish a task, you needed to type out entire programs to do the job. If you needed to do the same work again, you could type the entire program again or place it in a loop. However, loops are most useful when you are repeating the same thing, but writing the same loop repeatedly in different parts of your program with slightly modified values in each one is not a sane way to live your life.

Python has functions that enable you to gather sections of code into more convenient groupings that can be called on when you have a need for them.

In this chapter you learn:

  • How to create and use your own functions.

  • You are given guidelines to help facilitate your thinking about how to create and structure your programs to use functions.

  • How to write your functions so that you can later interrogate them for information about how they behave and what you intend for them to do.

Putting Your Program into Its Own File

As the examples in this book get longer, typing the entire code block begins to be a burden. A single mistake causes you to retype in the entire block of code you are working on. Long before you've gotten to the point where you have more than, say, 40 lines of code to type, you are unlikely to want to have to do it more than once.

You are probably already aware that programmers write programs that are saved as source code into files that can be opened, edited, and run without a great deal of work.

To reach this far more convenient ...

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