Word to the wise: learn how _PyString_Resize works. I just fixed dozens of
misues in the code base, and beefed up the docs. Here's the checkin
comment:
"""
Repair widespread misuse of _PyString_Resize. Since it's clear people
don't understand how this function works, also beefed up the docs. The
most common usage error is of this form (often spread out across gotos):
if (_PyString_Resize(&s, n) < 0) {
Py_DECREF(s);
s = NULL;
goto outtahere;
}
The error is that if _PyString_Resize runs out of memory, it automatically
decrefs the input string object s (which also deallocates it, since its
refcount must be 1 upon entry), and sets s to NULL. So if the "if"
branch ever triggers, it's an error to call Py_DECREF(s): s is already
NULL! A correct way to write the above is the simpler:
if (_PyString_Resize(&s, n) < 0)
goto outtahere;
"""
Even better, *most* of the time you can just do
_PyString_Resize(&s, n);
return s;
at the end of a function. This works correctly in all respects regardless
of whether _PyString_Resize() succeeds or fails.
Note that there's also no need to store a trailing \0 byte yourself before
calling _PyString_Resize: it does that automatically (for all the PyString_
alloc and realloc functions, the size you pass in is one less than the
number of bytes actually allocated for string space, and a trailing \0 byte
is always appended by magic in successful cases).
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