[Python-Dev] Convert int() to size_t in Python/C (original) (raw)

Martin Panter vadmium+py at gmail.com
Fri Apr 29 19:42:03 EDT 2016

On 29 April 2016 at 18:11, Marcos Dione <mdione at grulic.org.ar> wrote:

On Fri, Apr 29, 2016 at 12🔞46PM -0400, Random832 wrote:

On Fri, Apr 29, 2016, at 10:45, Marcos Dione wrote: > One possible solution hat was suggested to me in the #python IRC > channel was to use that, then test if the resulting value is negative, > and adjust accordingly, but I wonder if there is a cleaner, more general > solution (for instance, what if the type was something else, like lofft, > although for that one in particular there is a convertion > function/macro).

In principle, you could just use PyLongAsUnsignedLong (or LongLong), and raise OverflowError manually if the value happens to be out of sizet's range. (99% sure that on every linux platform unsigned long is the same size as sizet. But it's not like it'd be the first function in OS to call a system call that takes a sizet. Read just uses Pyssizet. Write uses the buffer protocol, which uses Pyssizet. How concerned are you really about the lost range here? What does the system call return (its return type is ssizet) if it writes more than SSIZEMAX bytes? (This shouldn't be hard to test, just try copying a >2GB file on a 32-bit system)

I would probably just use Py_ssize_t, since that is what the return value is. Otherwise, a large positive count input could return a negative value, which would be inconsistent, and could be mistaken as an error.

It's a very good point, but I don't have any 32 bits systems around with a kernel-4.5. I'll try to figure it out and/or ask in the kernel ML.

Maybe you can compile a 32-bit program and run it on a 64-bit computer (gcc -m32).

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