Automatic Boolean casting

Using an if statement with a non-Boolean type will cast it to a Boolean. In other words, the following two statements are always equivalent:

if a:
 ...
if bool(a): # exactly the same as above
 ...

A typical example is testing whether a list is empty:

# L is a list
if L:
    print("list not empty")
else:
    print("list is empty")

An empty list, or tuple, will return False.

You can also use a variable in the if statement, for example, an integer:

# n is an integer
if n % 2:         # the modulo operator
    print("n is odd")
else:
    print("n is even")

Note that we used % for the modulo operation, which returns the remainder of an integer division. In this case, it returns 0 or 1 as the remainder after modulo 2.

In this last example, the values 0 or 1 are cast to bool; see also Section 2.3.4, Booleans and integers.

The Boolean operators or, and, and not will also implicitly convert some of their arguments to a Boolean.