[Python-Dev] Python 2.4 extensions require VC 7.1? (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Sat Jun 17 14:19:19 CEST 2006

Kristján V. Jónsson wrote:

I remember you voicing this point at the Texas sprint. I can't say I agree. The behaviour of certain function (like signal and fopen) is undefined for certain arguments. Undefined is undefined, exiting the program with an admonition is one of the possible outcomes (as is formatting your hard drive.)

For fopen(3), you are right. For signal(3), VS2005 is in clear violation with ISO C, which specifies in 7.14.1.1

   [#8] If the request can  be  honored,  the  signal  function
   returns  the  value  of  func for the most recent successful
   call to signal for the specified signal sig.   Otherwise,  a
   value  of SIG_ERR is returned and a positive value is stored
   in errno.

The set of acceptable signals is deliberately implementation-defined, and it is consequential that an attempt to set an unsupported signal gives an error (ISO C cannot specify that the error is EINVAL, since EINVAL is not part of ISO C).

In my opinion this is to be considered "a good thing" since it helps us adhere to the "defined" parts of the standards and not rely on something which is utterly unknown or unpredictable by the standards (but which happens to work on some platforms, no thanks to the standards.) Besides, we only found this an issue in three places: signal(), fopen() and strftime() functions. Not a huge thing to fix.

For fopen and strftime, they could have achieved the same effect with just setting errno to EINVAL. The C runtime library just should never ever terminate the program unless explicitly asked to, just as Python should never ever terminate execution without giving the application a chance to intervene (e.g. by catching an exception).

VS2005 also can create binaries for the X64 windows platform, no small point, and the primary reason we started using it in the first place.

OTOH, you don't need VS2005 to create AMD64 binaries. I had been creating Itanium binaries for several years now with VS2003, and started producing AMD64 binaries for Python 2.5.

Regards, Martin

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