False or None vs. None or False

python boolean-logic
Virgiliu picture Virgiliu · Oct 12, 2010 · Viewed 77k times · Source 
In [20]: print None or False
-------> print(None or False)
False

In [21]: print False or None
-------> print(False or None)
None

This behaviour confuses me. Could someone explain to me why is this happening like this? I expected them to both behave the same.

Answer

RichieHindle picture RichieHindle · Oct 12, 2010

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).

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