This chapter presents the Python
if statement, which is the main statement used
for selecting from alternative actions based on test results. Because
this is our first in-depth look at compound statements—statements that
embed other statements—we will also explore the general concepts behind
the Python statement syntax model here in more detail than we did in the
introduction in Chapter 10.
if statement introduces
the notion of tests, this chapter will also deal with Boolean
expressions and fill in some details on truth tests in general.
In simple terms, the Python
if statement selects actions to perform.
It’s the primary selection tool in Python and represents much of the
logic a Python program possesses. It’s also our
first compound statement. Like all compound Python statements, the
if statement may contain other
statements, including other
fact, Python lets you combine statements in a program sequentially (so
that they execute one after another), and in an arbitrarily nested
fashion (so that they execute only under certain conditions).
if statement is typical of
if statements in most procedural
languages. It takes the form of an
if test, followed by one or more optional
elif (“else if”) tests and a final optional
else block. The tests and the
else part each have an associated
block of nested statements, indented under a header line. When the
if statement runs, Python executes the block ...