Program Arcade Games: With Python and Pygame, Fourth Edition

CHAPTER 20

Recursion

A child couldn’t sleep, so her mother told her a story about a little frog,

who couldn’t sleep, so the frog’s mother told her a story about a little bear,

  who couldn’t sleep, so the bear’s mother told her a story about a little weasel…

   who fell asleep.

  …and the little bear fell asleep;

…and the little frog fell asleep;

…and the child fell asleep.

(Source: http://everything2.com/title/recursion)

Recursion is an object or process that is defined in terms of itself. Mathematical patterns such as factorials and the Fibonacci series are recursive. Documents that can contain other documents, which themselves can contain ...