def find_source(self, filename):
        source = None

        base, ext = os.path.splitext(filename)
        TRY_EXTS = {
            '.py':  ['.py', '.pyw'],
            '.pyw': ['.pyw'],
        }
        try_exts = TRY_EXTS.get(ext)
        if not try_exts:
            return filename, None

        for try_ext in try_exts:
            try_filename = base + try_ext
            if os.path.exists(try_filename):
                return try_filename, None
            source = self.coverage.file_locator.get_zip_data(try_filename)
            if source:
                return try_filename, source
        raise NoSource("No source for code: '%s'" % filename)
Test we can follow a m2m and another m2m
dataset/ETHPy150Open RoseOu/flasky/venv/lib/python2.7/site-packages/coverage/results.py/Analysis.find_source--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.5/tests/modeltests/prefetch_related/tests.py/PrefetchRelatedTests.test_m2m_then_m2m