Python evaluates 0 as False

Question

In the Python console:

>>> a = 0
>>> if a:
...   print \"L\"
... 
>>> a = 1
>>> if a:
...   print \"L\"
... 
L
>>&g         


        

Answer 1

First of all, everything in python is an object. Therefore, your 0 is also an object, specifically, a built-in object.

Here are the built-in objects considered as false:

1. constants defined to be false: None and False.
2. zero of any numeric type: 0, 0.0, 0j, Decimal(0), Fraction(0, 1)
3. empty sequences and collections: '', (), [], {}, set(), range(0)

So when you put 0 in an if or while condition, or in a Boolean operation, it is tested for truth value.

# call the __bool__ method of 0
>>> print((0).__bool__())
False

# 
>>> if not 0:
...     print('if not 0 is evaluated as True')
'if not 0 is evaluated as True'