instance: A member of a set. The TurtleWorld in this chapter is a member of the set of TurtleWorlds.
loop: A part of a program that can execute repeatedly.
encapsulation: The process of transforming a sequence of statements into a function deﬁnition.
generalization: The process of replacing something unnecessarily speciﬁc (like a number) with something appropriately general (like a variable or parameter).
keyword argument: An argument that includes the name of the parameter as a “keyword.”
interface: A description of how to use a function, including the name and descriptions of the arguments and return value.
refactoring: The process of modifying a working program to improve function interfaces and other qualities of the code.
development plan: A process for writing programs.
docstring: A string that appears in a function deﬁnition to document the function’s inter face.
precondition: A requirement that should be satisﬁed by the caller before a function starts.
postcondition: A requirement that should be satisﬁed by the function before it ends.