Why functions - Not only for python

It may not be clear why it is worth the trouble to divide a program into functions. There are a lot of reasons; here are few:

• Creating a new function gives you an opportunity to name a group of statements, which makes your program easier to read and debug.
• Functions can make a program smaller by eliminating repetitive code. Later, if you make a change, you only have to make it in one place.
• Dividing a long program into functions allows you to debug the parts one at a time and then assemble them into a working whole.
• Well-designed functions are often useful for many programs. Once you write and debug one, you can reuse it.

from Thinking in python