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Comment #1 on issue 2832 by [email protected]: bool(Relational) should
raise ValueError
http://code.google.com/p/sympy/issues/detail?id=2832
There are some serious inconsistencies going on here. The problem is that
we are lazy about relational evaluation, passing > and >= to < and <=. In
fact, those are respectively for Number, even though that is **wrong**:
def __gt__(self, other):
return _sympify(other).__lt__(self)
def __ge__(self, other):
return _sympify(other).__le__(self)
(I believe this is not causing serious problems because all the subclasses
currently override these methods).
But even without that bug, this leads to inconsistencies, especially with
nan, which tries to make all comparisons False, like
In [86]: nan > 0
Out[86]: False
In [87]: nan >= 0
Out[87]: True
In [98]: oo > nan
Out[98]: True
In [99]: nan < oo
Out[99]: False
Also, comparisons against complex numbers are allowed, even though these
can never be made to be consistant (at least arithmetically, but as you can
see with nan, it's not so easy to make these things transitively
consistant).
So part of the issue here is to raise ValueError also for comparisons of
non-real numbers (real here includes +/- oo).
Question: should we raise ValueError for things like I > x?
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