Comment #2 on issue 3635 by [email protected]: Backwards compatibility
with old assumptions
http://code.google.com/p/sympy/issues/detail?id=3635
The only compatibility we need to care about is the API. So things like
Symbol('x', positive=True) and x.is_positive. The latter is easy: just
make it a shortcut to ask(Q.positive(x)). The former is a bit more
tricky. I guess we are going to have to drop the convention that
Symbol('x') != Symbol('x', positive=True).
So what will be the best thing to do? Symbol('x', positive=True) will have
to globally assume that x is positive? Should we raise a warning/error if
someone does
x1 = Symbol('x', positive=True)
x2 = Symbol('x', negative=True)
Should we deprecate that API? I think we really need to figure out exactly
how global assumptions are going to work, if at all.
Another issue is regarding specifics of the assumptions system. For
example, do we want ask(Q.positive(oo)) to return True. Before you
say "yes", look at issue 2877.
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