[pypy-dev] Findings in the Cython test suite

[Stefan Behnel]

Stefan Behnel, 02.04.2012 10:35:
> There is one major problem that accounts for the bulk of the test failures,
> somehow related to frame handling. You can tell by the huge amount of long
> traceback sequences that run into StackOverflowErrors and equivalent
> RuntimeErrors.

I found one test that, when run all by itself, triggers a RuntimeError,
boldly claiming that it reached the maximum recursion depth after a couple
of calls. There do not seem to be any frames or tracebacks involved up to
that point.

The test executes a C representation of the following code, run as a doctest:

'''
class A:
    def append(self, x):
        print u"appending"
        return x

def test_append(L):
    """
    >>> test_append(A())
    """
    print L.append(1)
'''

(The background is that Cython optimistically replaces calls to
obj.append() by code that assumes that obj is a list, so this tests the
failure of that assumption)

It gives me this error:

"""
    Traceback (most recent call last):
      File ".../pypy/lib-python/2.7/doctest.py", line 1254, in __run
        compileflags, 1) in test.globs
      File "<doctest append.__test__.test_append (line 11)[1]>", line 1, in
<module>
        _ = test_append(A())
      File "append.pyx", line 34, in append.test_append (append.c:930)
    RuntimeError: maximum recursion depth exceeded
"""

The same happens when I call it manually, i.e.

    import append; append.test_append(append.A())

The basic C code that gets executed in the test_append() function is simply

    PyObject* m = PyObject_GetAttrString(L, "append");
    r = PyObject_CallFunctionObjArgs(m, x, NULL);

And that's where the error gets raised (returning r==NULL). Specifically,
it does not enter into the actual append() method but fails before that,
right at the call.

I put a copy of the generated C file here:

http://consulting.behnel.de/append.tgz

Could someone shed some light on this?

Stefan