Hi,
I noticed that Robert used the PY_NEW() hack in the Alioth shootout
implementations, which got me into rethinking how to deal with this. I know
that it's faster and all that, so there's a need to do this. However, I
dislike the fact that one needs to write a header file and a cdef-external
declaration just to get to this feature.
To fix this, I pushed a change that optimises this
cdef type some_type = ...
obj = some_type.__new__(some_type)
into a call to the tp_new slot. It requires that the name is used twice
(just like it works in Python), and it also requires the object to be
either declared as 'type' or be the name of an extension type. This is
because Python does the type checking in the Python __new__() method, not
in the slot function, so we have to make sure this optimisation doesn't
lead to errors being ignored that would otherwise be caught by a real call
to __new__().
I think this is safe, but I wanted to mention it here so that others can
give it another bit of thought.
I know that there are better ways to do this behind the scenes. If we know
that an extension type (hierarchy) does not define __init__(), we can even
optimise a simple type instantiation call into a tp_new() call. However,
the above is an explicit way of doing it, it's the normal Python spelling,
and it doesn't prevent further optimisations in the future. So I think it's
worth it.
Stefan
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