Status: Accepted
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 2832 by [email protected]: bool(Relational) should raise
ValueError
http://code.google.com/p/sympy/issues/detail?id=2832
This has been discussed before, but I didn't find an explicit issue for it,
so here it is.
This is very closely related to issue 1887, and I kind of doubt it can be
fixed correctly without fixing that first.
There are some places in the code with tests like
if x > 3:
do stuff
implicitly assuming x is a number. But if x is a Symbol, which is all to
easy to pass to a function in SymPy, this will silently work:
In [17]: bool(x > 3)
Out[17]: True
Thus, we have problems like issue 1740.
I think that we should make bool(Relational) raise ValueError, unless we
can explicitly determine from the assumptions if it is True or False (in
other words, if the assumptions give None, raise an error). This will
prevent hidden bugs like the above, and will also fit in with the Python 3
standard that you should not be able to compare incomparable types.
See also the discussion at
https://github.com/sympy/sympy/pull/695#issuecomment-2651875.
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