Why is the destructor called when the CPython garbage collector is disabled?
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by Frederik
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Published on 2010-04-05T11:28:14Z
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2010/04/05
11:33 UTC
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I'm trying to understand the internals of the CPython garbage collector, specifically when the destructor is called. So far, the behavior is intuitive, but the following case trips me up:
- Disable the GC.
- Create an object, then remove a reference to it.
- The object is destroyed and the __del__ method is called.
I thought this would only happen if the garbage collector was enabled. Can someone explain why this happens? Is there a way to defer calling the destructor?
import gc
import unittest
_destroyed = False
class MyClass(object):
def __del__(self):
global _destroyed
_destroyed = True
class GarbageCollectionTest(unittest.TestCase):
def testExplicitGarbageCollection(self):
gc.disable()
ref = MyClass()
ref = None
# The next test fails.
# The object is automatically destroyed even with the collector turned off.
self.assertFalse(_destroyed)
gc.collect()
self.assertTrue(_destroyed)
if __name__=='__main__':
unittest.main()
Disclaimer: this code is not meant for production -- I've already noted that this is very implementation-specific and does not work on Jython.
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