[Python-Dev] Pep 353: Py_ssize_t advice

[David Abrahams]

Pep 353 advises the use of this incantation:

  #if PY_VERSION_HEX < 0x02050000
  typedef int Py_ssize_t;
  #define PY_SSIZE_T_MAX INT_MAX
  #define PY_SSIZE_T_MIN INT_MIN
  #endif

I just wanted to point out that this advice could lead to library
header collisions when multiple 3rd parties decide to follow it.  I
suggest it be changed to something like:

  #if PY_VERSION_HEX < 0x02050000 && !defined(PY_SSIZE_T_MIN)
  typedef int Py_ssize_t;
  #define PY_SSIZE_T_MAX INT_MAX
  #define PY_SSIZE_T_MIN INT_MIN
  #endif

(C++ allows restating of typedefs; if C allows it, that should be
something like):

  #if PY_VERSION_HEX < 0x02050000
  typedef int Py_ssize_t;
  # if !defined(PY_SSIZE_T_MIN)
  #  define PY_SSIZE_T_MAX INT_MAX
  #  define PY_SSIZE_T_MIN INT_MIN
  # endif
  #endif

You may say that library developers should know better, but I just had
an argument with a very bright guy who didn't get it at first.

Thanks, and HTH.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com