[Python-Dev] PEP: Adding data-type objects to Python (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Wed Nov 1 21:05:28 CET 2006

Travis E. Oliphant schrieb:

I was too hasty. There are some things actually missing from ctypes:

I think Thomas can correct me if I'm wrong: I think endianness is supported (although this support seems undocumented). There seems to be code that checks for the presence of a byteswapped attribute on fields of a struct; presence of this field is then interpreted as data having the "other" endianness.

1) long double (this is not the same across platforms, but it is a data-type).

That's indeed missing.

2) complex-valued types (you might argue that it's just a 2-array of floats, but you could say the same thing about int as an array of bytes). The point is how do people interpret the data. Complex-valued data-types are very common. It is one reason Fortran is still used by scientists.

Well, by the same reasoning, you could argue that pixel values (RGBA) are missing in the PEP. It's a convenience, sure, and it may also help interfacing with the platform's FORTRAN implementation - however, are you sure that NumPy's complex layout is consistent with the platform's C99 _Complex definition?

3) Unicode characters

4) What about floating-point representations that are not IEEE 754 4-byte or 8-byte.

Both of these are available in a platform-dependent way: if the platform uses non-IEEE754 formats for C float and C double, ctypes will interface with that just fine. It is actually vice versa: IEEE-754 4-byte and 8-byte is not supported in ctypes. Same for Unicode: the platform's wchar_t is supported (as you said), but not a platform-independent (say) 4-byte little-endian.

Regards, Martin

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