New submission from Xavier de Gaye:
The following debugging session, run with python on the default branch, shows
that pdb does not stop in __del__ when it is invoked.
The reason is:
- The destructor is not called when processing the 'c = 1' statement because
foo frame.f_locals owns a reference to the C instance.
- When the interpreter is about to invoke the trace function with the ensuing
debug event, the call to PyFrame_LocalsToFast in call_trampoline causes the
destructor to be invoked (as shown by gdb), and the destructor is not traced
because at that time tstate->use_tracing is false.
This is confirmed by the fact that when 'c = 1' is replaced with
'c = 1; locals()' (on one single line so as not to trigger the trace function
before the call to locals()), then pdb stops in __del__.
=== foo.py ================
class C:
def __del__(self):
print("Calling C destructor.")
def foo():
c = C()
import pdb; pdb.set_trace()
c = 1
foo()
===============================
$ ./python /tmp/foo.py
> /tmp/foo.py(8)foo()
-> c = 1
(Pdb) step
Calling C destructor.
--Return--
> /tmp/foo.py(8)foo()->None
-> c = 1
(Pdb)
===============================
----------
components: Interpreter Core
messages: 177240
nosy: xdegaye
priority: normal
severity: normal
status: open
title: reference kept in f_locals prevents the tracing/profiling of a destructor
type: behavior
versions: Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue16653>
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