[Python-ideas] __contains__=None (was: __iter__ implies __contains__?)

Nick Coghlan dixit (2011-10-03, 18:00): [...]

duck-typed check for __contains__ would break for classes that explicitly raise TypeError, as is proposed for _BaseIO).

Maybe there should be possible to explicitly disallow the 'in' test by setting __contains__ to None (similar to already settled __hash__=None for non-hashables). Cheers. *j