Question

I found this kind of expression several times in a python program:

if variable is not None:
    dothings(variable)

It seems strange to me, and I think that it has no more sense than:

if variable:
    dothings(variable)

Maybe I don’t know Python enough, and the expression is explained somewhere?

Answer 1

variable could be 0, or False, or [], or (); be ‘falsy’ in other words, and then the if statement would be skipped.

See Truth testing for more detail on what is considered false in a boolean context.

In short, testing if variable is not None allows variable to be anything else, including values that would otherwise be considered False in a boolean context.