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Relational operators always evaluate to True when cast to bool #312

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mlangiu opened this issue Mar 3, 2020 · 2 comments · May be fixed by #354
Open

Relational operators always evaluate to True when cast to bool #312

mlangiu opened this issue Mar 3, 2020 · 2 comments · May be fixed by #354

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@mlangiu
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mlangiu commented Mar 3, 2020 •
edited

With the current version of symengine (symengine-0.6.0) the following returns True

import symengine as se

x = se.S('x')
expr = se.Eq(x, 0)
print(bool(expr))

The outcome I expected was a TypeError as in sympy
@qthequartermasterman
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This is not a resolution to this issue, but is a useful workaround for some cases. If both sides of the expression can be evaluated (i.e. checking if 0==sqrt(2)), then running bool(expr.simplify()) will return False if the equality is indeed false.
This is not ideal for speed purposes, because as far as I can tell, it uses sympy's simplify features to do the simplification.

This does not help in the case that either side does not simplify, like in the original post.

qthequartermasterman added a commit to qthequartermasterman/symengine.py that referenced this issue Jun 5, 2021
@qthequartermasterman
Override __bool__ in Relational, so that it returns whatever the bool…
a96e507 
…ean evaluation is, instead of always True. Resolves symengine#312
@qthequartermasterman qthequartermasterman linked a pull request Jun 5, 2021 that will close this issue
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@qthequartermasterman
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This is fixed in PR #354. That Pull Request raises a TypeError if there are free variables, and will return True or False depending on the simplification of the relational if there are no free variables.

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Evaluate Relationals when casting to bool qthequartermasterman/symengine.py
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@mlangiu @qthequartermasterman