Raymond Hettinger, 18.04.2011 19:26:
On Apr 18, 2011, at 10:11 AM, Maciej Fijalkowski wrote:
* we usually target CPython version that's already frozen, which is
pretty inconvinient to post this changes back. Example would be a
socket module where it has changed enough in 3.x that 2.7 changes make
no sense.
Do you have any thoughts on the problem with the concrete C API
not working well with subclasses of builtin types?
I'm thinking that the PEP should specifically ban the practice
of using the concrete api unless it is known for sure that
an object is an exact type match.
Absolutely.
It is okay to write PyList_New() followed by PyList_SetItem()
but not okay to use PyList_SetItem() on a user supplied
argument that is known to be a subclass of list. A fast path
can be provided for an exact path, but there would also need
to a be a slower path that either converts the object to
an exact list or that uses PyObject_SetItem().
For what it's worth, Cython generates code that contains optimistic
optimisations for common cases, such as iteration, x.append() calls, etc.
When it finds such a pattern, it generates separate code paths for the most
likely (builtin type) case and a slower fallback for the more unlikely case
of a user provided type. So you get both speed and compatibility for free,
just by writing idiomatic code like "for item in some_iterable".
Stefan
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
http://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
