Time for action – deciding with the if statement

We can use the if statement in the following ways:

1. Check whether a number is negative as follows:

   >>> if 42 < 0:
   ...     print('Negative')
   ... else:
   ...     print('Not negative')
   ...
   Not negative
   

   In the preceding example, Python decided that 42 is not negative. The else clause is optional. The comparison operators are equivalent to the ones in C++, Java, and similar languages.

2. Python also has a chained branching logic compound statement for multiple tests similar to the switch statement in C++, Java, and other programming languages. Decide whether a number is negative, 0, or positive as follows:

   >>> a = -42
   >>> if a < 0:
   ...     print('Negative')
   ... elif a == 0:
   ...     print('Zero')
   ... else:
   ...     print('Positive')
   ...
   Negative
   

   This time, Python decided that 42 is negative.

What just happened?

We learned how to do branching logic in Python.