Understanding False Values in Python: None, “False”, and 0

When working with conditional statements in Python, it’s important to understand what values evaluate to True and what values evaluate to False. While some values are obviously True, such as any non-zero number or a non-empty string, there are a few other values that can sometimes trip up programmers. In particular, the values None, "False", and the number 0 are all examples of values that evaluate to False in Python.

Let’s take a closer look at each of these values and why they evaluate to False.

None

In Python, None is a special value that represents the absence of a value. It’s often used to indicate that a variable or function argument has not been assigned a value, or to represent the result of a function that doesn’t return anything. When you use bool(None) to check if None is True or False, it will always evaluate to False.

x = None

if x:
    print("This won't be printed")
else:
    print("x is None")

“False”

The string "False" may seem like it would evaluate to True, since it contains the word “false”. However, in Python, a non-empty string always evaluates to True, regardless of its contents. Therefore, the string "False" is not the same as the boolean value False, and it will evaluate to True in conditional statements.

x = "False"
if x:
    print("x is non-empty string")
else:
    print("This won't be printed")

0

The number 0 may seem like it would evaluate to True, since it’s a non-empty value. However, in Python, any numeric value that is equal to 0 will evaluate to False. This includes integers, floats, and other numeric types.

x = 0
if x:
    print("This won't be printed")
else:
    print("x is 0")

It’s important to keep in mind that while these values evaluate to False, they still have a value that can be used in your code. For example, you can assign None to a variable, or use 0 in a calculation. Just be sure to use them in the appropriate context so that your code behaves as expected.

In conclusion, when writing conditional statements in Python, it’s important to be aware of values that evaluate to False, including None, “False”, and the number 0. You can write more robust and reliable code by understanding how these values behave.