http://svn.python.org/view/python/trunk/Python/ast.c?
rev=41486&view=markup

function ast_error_finish

It first gets the errstr, for a possible early out.
If there is an error string, it is increfed, but it is 
not decrefed on the other early outs.  (lineno==-1 and 
failure to build a tmp.


"""
    Py_INCREF(errstr);
    lineno = PyInt_AsLong(PyTuple_GetItem(value, 1));
    if (lineno == -1)
return;
    Py_DECREF(value);

    loc = PyErr_ProgramText(filename, lineno);
    if (!loc) {
Py_INCREF(Py_None);
loc = Py_None;
    }
    tmp = Py_BuildValue("(ziOO)", filename, lineno, 
Py_None, loc);
    Py_DECREF(loc);
    if (!tmp)
return;
    value = Py_BuildValue("(OO)", errstr, tmp);
    Py_DECREF(errstr);
"""

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ISTM that we don't need the INCREF or DECREF for errstr.  Do
you agree?

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No, though it took me a *long* time to see why, because the 
&value pointer is reused.

As best I understand it, PyErr_Fetch may leave (the initial 
value of) value with the only reference to errstr.

There is a Py_DECREF(value) after successfully retrieving a 
line number, but before using errstr to build the (new value 
of) value for PyErr_Restore.

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You are correct.  I thought I had tested, but test_grammar
failed with my removal.  I added the DECREFs.

Committed revision 41641.

Thanks for tracking this down.