The if statement is used for conditional execution:
if_stmt: "if" condition ":" suite
("elif" condition ":" suite)*
["else" ":" suite]
It selects exactly one of the suites by evaluating the conditions one
by one until one is found to be true (see section 
for
the definition of true and false); then that suite is executed (and no
other part of the if statement is executed or evaluated). If
all conditions are false, the suite of the else clause, if
present, is executed.