> If I understood correctly, you don't want the value to be truncated if the variable grows between the two calls to confstr(). Which behaviour would you expect? A Python exception?

A return size larger than the buffer is *supposed* to indicate
that the current value is larger than the supplied buffer, so I
would just expect it to reallocate the buffer, call confstr()
again and return the new value, unless it was known that such a
situation indicated an actual problem.

In other words, I would not expect it to do anything special.  I
didn't write the original patch the way I did in order to fix
this (potential) bug - it just seemed like the most natural way
to write the code.