[Python-Dev] __contains__ hook

[Fred L. Drake, Jr.]

M.-A. Lemburg writes:
 > Shouldn't 'in' be a slot of the sequence methods ? I'd suggest
 > creating a new tp_flag bit and then extending tp_as_sequence

  Only if we want to restrict set-like behavior to sequences, and I
don't think that's clear, though it does mirror the current
situation.
  Regardless of the location of the slot, why should a flag be needed?
Testing the slot for NULL is necessary to avoid core dumps anyway.

 > plus of course add an abstract function to abstract.c:
 > 
 > 	PySequence_Contain(PyObject *container, PyObject *element)

  There's already PySequence_In(...); see:

	http://www.python.org/doc/current/api/sequence.html#l2h-135

  I'm inclined to add PyObject_In(...) (or ..._Contains(); I like
Contains better than In, but there's precedence for In and that's more 
important) and define the new slot on the Object using one of the
reserved spaces.  That allows a clean interface for "pure" sets that
don't have to "look like" sequences or mappings.

 > which uses the above slot after testing the tp_flag setting.
 > Python instances, lists, tuples should then support this new
 > slot. We could even sneak in support for dictionaries once we
 > decide whether semantics whould be 

  Bait!


  -Fred

--
Fred L. Drake, Jr.	  <fdrake at acm.org>
Corporation for National Research Initiatives