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34 results

topics.py

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  • test_frame.py 9.54 KiB
    import gc
    import re
    import sys
    import types
    import unittest
    import weakref
    
    from test import support
    
    
    class ClearTest(unittest.TestCase):
        """
        Tests for frame.clear().
        """
    
        def inner(self, x=5, **kwargs):
            1/0
    
        def outer(self, **kwargs):
            try:
                self.inner(**kwargs)
            except ZeroDivisionError as e:
                exc = e
            return exc
    
        def clear_traceback_frames(self, tb):
            """
            Clear all frames in a traceback.
            """
            while tb is not None:
                tb.tb_frame.clear()
                tb = tb.tb_next
    
        def test_clear_locals(self):
            class C:
                pass
            c = C()
            wr = weakref.ref(c)
            exc = self.outer(c=c)
            del c
            support.gc_collect()
            # A reference to c is held through the frames
            self.assertIsNot(None, wr())
            self.clear_traceback_frames(exc.__traceback__)
            support.gc_collect()
            # The reference was released by .clear()
            self.assertIs(None, wr())
    
        def test_clear_does_not_clear_specials(self):
            class C:
                pass
            c = C()
            exc = self.outer(c=c)
            del c
            f = exc.__traceback__.tb_frame
            f.clear()
            self.assertIsNot(f.f_code, None)
            self.assertIsNot(f.f_locals, None)
            self.assertIsNot(f.f_builtins, None)
            self.assertIsNot(f.f_globals, None)
    
        def test_clear_generator(self):
            endly = False
            def g():
                nonlocal endly
                try:
                    yield
                    self.inner()
                finally:
                    endly = True
            gen = g()
            next(gen)
            self.assertFalse(endly)
            # Clearing the frame closes the generator
            gen.gi_frame.clear()
            self.assertTrue(endly)
    
        def test_clear_executing(self):
            # Attempting to clear an executing frame is forbidden.
            try:
                1/0
            except ZeroDivisionError as e:
                f = e.__traceback__.tb_frame
            with self.assertRaises(RuntimeError):
                f.clear()
            with self.assertRaises(RuntimeError):
                f.f_back.clear()
    
        def test_clear_executing_generator(self):
            # Attempting to clear an executing generator frame is forbidden.
            endly = False
            def g():
                nonlocal endly
                try:
                    1/0
                except ZeroDivisionError as e:
                    f = e.__traceback__.tb_frame
                    with self.assertRaises(RuntimeError):
                        f.clear()
                    with self.assertRaises(RuntimeError):
                        f.f_back.clear()
                    yield f
                finally:
                    endly = True
            gen = g()
            f = next(gen)
            self.assertFalse(endly)
            # Clearing the frame closes the generator
            f.clear()
            self.assertTrue(endly)
    
        def test_lineno_with_tracing(self):
            def record_line():
                f = sys._getframe(1)
                lines.append(f.f_lineno-f.f_code.co_firstlineno)
    
            def test(trace):
                record_line()
                if trace:
                    sys._getframe(0).f_trace = True
                record_line()
                record_line()
    
            expected_lines = [1, 4, 5]
            lines = []
            test(False)
            self.assertEqual(lines, expected_lines)
            lines = []
            test(True)
            self.assertEqual(lines, expected_lines)
    
        @support.cpython_only
        def test_clear_refcycles(self):
            # .clear() doesn't leave any refcycle behind
            with support.disable_gc():
                class C:
                    pass
                c = C()
                wr = weakref.ref(c)
                exc = self.outer(c=c)
                del c
                self.assertIsNot(None, wr())
                self.clear_traceback_frames(exc.__traceback__)
                self.assertIs(None, wr())
    
    
    class FrameAttrsTest(unittest.TestCase):
    
        def make_frames(self):
            def outer():
                x = 5
                y = 6
                def inner():
                    z = x + 2
                    1/0
                    t = 9
                return inner()
            try:
                outer()
            except ZeroDivisionError as e:
                tb = e.__traceback__
                frames = []
                while tb:
                    frames.append(tb.tb_frame)
                    tb = tb.tb_next
            return frames
    
        def test_locals(self):
            f, outer, inner = self.make_frames()
            outer_locals = outer.f_locals
            self.assertIsInstance(outer_locals.pop('inner'), types.FunctionType)
            self.assertEqual(outer_locals, {'x': 5, 'y': 6})
            inner_locals = inner.f_locals
            self.assertEqual(inner_locals, {'x': 5, 'z': 7})
    
        def test_clear_locals(self):
            # Test f_locals after clear() (issue #21897)
            f, outer, inner = self.make_frames()
            outer.clear()
            inner.clear()
            self.assertEqual(outer.f_locals, {})
            self.assertEqual(inner.f_locals, {})
    
        def test_locals_clear_locals(self):
            # Test f_locals before and after clear() (to exercise caching)
            f, outer, inner = self.make_frames()
            outer.f_locals
            inner.f_locals
            outer.clear()
            inner.clear()
            self.assertEqual(outer.f_locals, {})
            self.assertEqual(inner.f_locals, {})
    
        def test_f_lineno_del_segfault(self):
            f, _, _ = self.make_frames()
            with self.assertRaises(AttributeError):
                del f.f_lineno
    
    
    class ReprTest(unittest.TestCase):
        """
        Tests for repr(frame).
        """
    
        def test_repr(self):
            def outer():
                x = 5
                y = 6
                def inner():
                    z = x + 2
                    1/0
                    t = 9
                return inner()
    
            offset = outer.__code__.co_firstlineno
            try:
                outer()
            except ZeroDivisionError as e:
                tb = e.__traceback__
                frames = []
                while tb:
                    frames.append(tb.tb_frame)
                    tb = tb.tb_next
            else:
                self.fail("should have raised")
    
            f_this, f_outer, f_inner = frames
            file_repr = re.escape(repr(__file__))
            self.assertRegex(repr(f_this),
                             r"^<frame at 0x[0-9a-fA-F]+, file %s, line %d, code test_repr>$"
                             % (file_repr, offset + 23))
            self.assertRegex(repr(f_outer),
                             r"^<frame at 0x[0-9a-fA-F]+, file %s, line %d, code outer>$"
                             % (file_repr, offset + 7))
            self.assertRegex(repr(f_inner),
                             r"^<frame at 0x[0-9a-fA-F]+, file %s, line %d, code inner>$"
                             % (file_repr, offset + 5))
    
    class TestIncompleteFrameAreInvisible(unittest.TestCase):
    
        def test_issue95818(self):
            #See GH-95818 for details
            import gc
            self.addCleanup(gc.set_threshold, *gc.get_threshold())
    
            gc.set_threshold(1,1,1)
            class GCHello:
                def __del__(self):
                    print("Destroyed from gc")
    
            def gen():
                yield
    
            fd = open(__file__)
            l = [fd, GCHello()]
            l.append(l)
            del fd
            del l
            gen()
    
    
        @support.cpython_only
        def test_sneaky_frame_object(self):
    
            def trace(frame, event, arg):
                """
                Don't actually do anything, just force a frame object to be created.
                """
    
            def callback(phase, info):
                """
                Yo dawg, I heard you like frames, so I'm allocating a frame while
                you're allocating a frame, so you can have a frame while you have a
                frame!
                """
                nonlocal sneaky_frame_object
                sneaky_frame_object = sys._getframe().f_back
                # We're done here:
                gc.callbacks.remove(callback)
    
            def f():
                while True:
                    yield
    
            old_threshold = gc.get_threshold()
            old_callbacks = gc.callbacks[:]
            old_enabled = gc.isenabled()
            old_trace = sys.gettrace()
            try:
                # Stop the GC for a second while we set things up:
                gc.disable()
                # Create a paused generator:
                g = f()
                next(g)
                # Move all objects to the oldest generation, and tell the GC to run
                # on the *very next* allocation:
                gc.collect()
                gc.set_threshold(1, 0, 0)
                # Okay, so here's the nightmare scenario:
                # - We're tracing the resumption of a generator, which creates a new
                #   frame object.
                # - The allocation of this frame object triggers a collection
                #   *before* the frame object is actually created.
                # - During the collection, we request the exact same frame object.
                #   This test does it with a GC callback, but in real code it would
                #   likely be a trace function, weakref callback, or finalizer.
                # - The collection finishes, and the original frame object is
                #   created. We now have two frame objects fighting over ownership
                #   of the same interpreter frame!
                sys.settrace(trace)
                gc.callbacks.append(callback)
                sneaky_frame_object = None
                gc.enable()
                next(g)
                # g.gi_frame should be the the frame object from the callback (the
                # one that was *requested* second, but *created* first):
                self.assertIs(g.gi_frame, sneaky_frame_object)
            finally:
                gc.set_threshold(*old_threshold)
                gc.callbacks[:] = old_callbacks
                sys.settrace(old_trace)
                if old_enabled:
                    gc.enable()
    
    
    if __name__ == "__main__":
        unittest.main()