False or None vs. None or False

The expression x or y evaluates to x if x is true, or y if x is false.

Note that "true" and "false" in the above sentence are talking about "truthiness", not the fixed values True and False. Something that is "true" makes an if statement succeed; something that's "false" makes it fail. "false" values include False, None, 0 and [] (an empty list).

The or operator returns the value of its first operand, if that value is true in the Pythonic boolean sense (aka its "truthiness"), otherwise it returns the value of its second operand, whatever it happens to be. See the subsection titled Boolean operations in the section on Expressions in the current online documentation.

In both your examples, the first operand is considered false, so the value of the second one becomes the result of evaluating the expression.

You must realize that None, False and True are all singletons.

For example, if foo is not None means that foo has some value other than None. This works the same as just having if foo which is basically if foo == True.

So, not None and True work the same way. Also, None and False work the same way.

>>> foo = not None>>> bool(foo)True>>> foo = 5  # Giving an arbitrary value here>>> bool(foo)True>>> foo = None>>> bool(foo)False>>> foo = 5  # Giving an arbitrary value here>>> bool(foo)True

The important thing to realize and to be aware of when coding is that when comparing two things, None needs is, but True and False need ==. Avoid if foo == None and do only if foo is None and avoid if foo != None and do only if foo is not None. In the case of if foo is not None, simply do if foo. In the case of if foo is None, simply do if not foo.

Note: True is basically 1 and False is basically 0. In the old days of Python, we had only 1 for a value of true and we had 0 for a value of false. It's more understandable and human-friendly to say True instead of 1 and more understandable and human-friendly to say False instead of 0.