Status: Accepted
Owner: ronan.l...@gmail.com
Labels: Type-Defect Priority-High
New issue 2389 by ronan.l...@gmail.com: Semantic inconsistency between
Basic.__contains__ and Tuple.__contains__
http://code.google.com/p/sympy/issues/detail?id=2389
According to the implementation in Basic.__contains__, 'A in B' means 'Is A
part of the expression tree for B?', but for objects that are naturally
considered containers, like Tuple or Set, 'A in B' means 'Is A an element
of B?'. These definitions are incompatible (consider '2 in Interval(1, 3)'
or 'x in Tuple(x+1, y)') and lumping them together with the same syntax is
bound to create difficult problems.
The problem with the first definition is that it confuses the object with
its expression tree, while they are considered nearly everywhere else in
sympy. Besides, there's already a method which has basically the same
meaning, .has(). So I think that Basic.__contains__ should just be removed
and its functionality merged with Basic.has().
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