UNINITIALIZED VARIABLES AND THE VALUE NONE IN PYTHON

Python distinguishes between an uninitialized variable and the value None. The former is a variable that has not been assigned a value, whereas the value None is a value that indicates “no value.” Collections and methods often return the value None, and you can test for the value None in conditional logic.

The next portion of this appendix shows you how to “slice and dice” text strings with built-in Python functions.