don't understand piece of code

[Paul Royik]

In Mul class I see this piece of code:

    def _eval_is_real(self):

        real = True

        zero = one_neither = False

        for t in self.args:

            if not t.is_complex:

                return t.is_complex

Don't understand last two lines. How is it possible that if t is not complex, then return that all Mul is not real?

[Mateusz Paprocki]

Hi,

I think this is because t.is_real implies t.is_complex, so saying
t.is_complex == False doesn't mean t.is_real == True; it means that t
is perhaps not a number (e.g. a MatrixExpr). As we employ three-valued
logic (yes, no, don't know), then returning t.is_complex is the
correct approach. Also see [1], because this code was originally wrong
(perhaps Chris can give you better explanation).

[1] https://github.com/sympy/sympy/commit/4d9c756d031e3965867701a65d3970a915495944

Mateusz

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[Paul Royik]

OK. Thanks.