[Python-Dev] PyRange_New() alternative?
Ralf W. Grosse-Kunstleve
rwgk at yahoo.com
Fri Jun 23 12:23:19 CEST 2006
--- Tim Peters <tim.peters at gmail.com> wrote:
> [Ralf W. Grosse-Kunstleve]
> > Thanks! This does the trick for me:
> > #if PY_VERSION_HEX >= 0x02030000
> > PyObject_CallFunction(
> > (PyObject*) &PyRange_Type, "lll", start, start+len*step, step)
> Note that this is extremely lax about possible overflow in the
> arithmetic. For that reason it can't be recommend for general use.
> > #else
> > PyRange_New(start, len, step, 1)
> > #endif
> > I've tested this with Python 2.2.3, 2.3.4, 2.4.3, 2.5b1. Python 2.2.3
> > WS 3) compiles the PyRange_Type call, but there is a runtime error:
> > TypeError: cannot create 'xrange' instances
> Sorry, I didn't follow that. The only mention of PyRange_Type in the
> #if'ed code above is in a block that looks like it should be entirely
> ignored in a 2.2.3 Python (provided you're using the right header
> files and the C compiler isn't broken).
First I tried the PyRange_Type code with Python 2.2.3 and no #ifdef. I resorted
to the #ifdef and the old PyRange_New() call only because it didn't work.
> Compile all of Python that way, and you'll probably see more of those
> than you can count ;-) Python is normally compiled with, and is
> _intended_ to be compiled with,
> If you didn't do that, try it.
I missed this. Thanks for pointing it out.
> Since it was never documented to begin with, it was a "use at your own
> risk" thing anyway. As you're currently it's only known user
> throughout all of history :-), if you do all the work of
> rehabilitating it, I'd be at best a weak -1 anyway: one of the
> problems with PyRange_New was that its signature was wildly different
> than the builtin range()'s. That made it a poor API for "surprise,
> surprise!" reasons alone. That was a mistake, and I'd rather
> inconvenience you than pass that mistake on to our precious children
I agree, although I find it hard to believe I am that unique. I'll google for
PyRange_New in a couple of years to see how many more people got stranded. :-)
Although it will bias the measure of my uniqueness, I still believe you should
tell people in the documentation what to do, e.g.
PyObject_CallFunction((PyObject*) &PyRange_Type, "lll", start, stop, step)
which avoids showing the sloppy start+len*step hack.
BTW: by the time my children pick up programming nobody under 30 will use C
Python anymore. ;-)
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