#14608: Symbolic functions break the __hash__ contract
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Reporter: vbraun | Owner: burcin
Type: defect | Status: new
Priority: major | Milestone: sage-5.10
Component: symbolics | Keywords:
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
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Equal objects must have the same hash if they are hashable
(http://docs.python.org/2/reference/datamodel.html#object.__hash__):
{{{
sage: my_func = function('func',nargs=1)
sage: f = my_func(0)
sage: bool(f == f.simplify())
True
sage: hash(f) == hash(f.simplify())
False
}}}
As reported on http://ask.sagemath.org/question/2587/simplify-shenanigans,
hash lookup errors then leads to undesirable behavior:
{{{
sage: ex = my_func(0) + my_func(1)
sage: ex.subs(my_func(0)==1)
func(1) + 1
sage: ex.simplify().subs(my_func(0)==1)
func(0) + func(1)
}}}
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14608>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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