[Python-Dev] Null checking

[David Abrahams]

A couple of quick questions for the authors of the Python source: I notice
that most, if not all, of the Python 'C' API includes null checks for the
PyObject* arguments, meaning that you can't crash Python by passing the
result of a previous operation, even if it returns an error.

First question: can that be counted on? Hmm, I guess I've answered my own
question -- PyNumber_InPlaceAdd has no checks.

I note that the null_error() check in abstract.c is non-destructive: it
preserves any existing error, whereas other checks (e.g. in typeobject.c)
do not.

Second question: I guess I really want to know what the intention behind
these checks is. Is it something like "prevent extension writers from
crashing Python in some large percentage of cases", or is there a deeper
plan that I'm missing?

TIA,
Dave

+---------------------------------------------------------------+
                  David Abrahams
      C++ Booster (http://www.boost.org)               O__  ==
      Pythonista (http://www.python.org)              c/ /'_ ==
  resume: http://users.rcn.com/abrahams/resume.html  (*) \(*) ==
          email: david.abrahams@rcn.com
+---------------------------------------------------------------+