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import gc
import sys
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_generator(self):
endly = False
def g():
nonlocal endly
try:
yield
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)
@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())
def test_main():
support.run_unittest(__name__)
if __name__ == "__main__":
test_main()
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