[Python-bugs-list] [ python-Bugs-496873 ] cPickle / time.struct_time loop

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Thu, 27 Dec 2001 10:02:23 -0800


Bugs item #496873, was opened at 2001-12-26 13:18
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Category: Type/class unification
Group: Python 2.2.1 candidate
Status: Open
Resolution: None
Priority: 5
Submitted By: Vicente Rey Bakaikoa (bixentxo)
Assigned to: Anthony Baxter (anthonybaxter)
Summary: cPickle / time.struct_time loop

Initial Comment:
The following code produces and endless loop
on python 2.2 ( ok on python 2.1 ). The
file being saved by cPickle.dump grows
indefinetely.

-----------------------------
import time, cPickle

created = time.localtime()

fd = open('/tmp/bla.pickle','w')
cPickle.dump(created,fd)
[...endless loop... ]

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>Comment By: Tim Peters (tim_one)
Date: 2001-12-27 10:02

Message:
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Re "does anybody need to pickle time structs?", I think a 
better question is "does anybody pickle time.localtime() 
results?".  The existence of the bug report suggests yes, 
and the OP is right that this worked in 2.1 (and 2.0, 
and ...).

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Comment By: Guido van Rossum (gvanrossum)
Date: 2001-12-27 08:32

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Actually, the bug was in copy_reg._reduce: it was possible
that this would not make any progress, returning an instance
of the same type that it was passed, thus causing the
infinite recursion. I've checked in a fix that raises an
exception when this situation is detected.
(copy_reg.py:1.10)

Now, the question is, does anybody need to pickle time
structs? I would recommend converting them into a tuple
before pickling: pickle.dumps(tuple(time.localtime())) works
fine.

The statvfs issue was an unrelated bug; I've checked in a
fix for that too. (posixmodule.c:2.217)

Both are 2.2.1 candidates (I only noted this in the
posixmodule.c CVS checkin message by mistake).

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Comment By: Guido van Rossum (gvanrossum)
Date: 2001-12-27 06:06

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It gets in an infinite loop with pickle too, so I think this
is definitely a bug in the magical type used for localtime.
The stacktrack looks like this:

  File "/usr/local/lib/python2.2/pickle.py", line 370, in
save_tuple
    save(element)
  File "/usr/local/lib/python2.2/pickle.py", line 215, in
save
    self.save_reduce(callable, arg_tup, state)
  File "/usr/local/lib/python2.2/pickle.py", line 241, in
save_reduce
    save(arg_tup)
  File "/usr/local/lib/python2.2/pickle.py", line 221, in
save
    f(self, object)

repeated an infinite number of times.

Note that we should look at the other objects that use
structseq.c/h too. pickle.dumps(os.stat("/")) gives

TypeError: constructor takes exactly 13 arguments (10 given)

pickle.dumps(os.statvfs("/")) gives

pickle.PicklingError: Can't pickle <type
'posix.statvfs_result'>: it's not the same object as
posix.statvfs_result

Looks like a variety of bugs. :-(



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Comment By: Michael Hudson (mwh)
Date: 2001-12-27 03:50

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Another factoid: if you back out the change that renamed the 
"struct_time" type to "time.struct_time", the crash goes 
away, to be replaced with 

cPickle.PicklingError: Can't pickle <type 'struct_time'>: 
it's not found as __builtin__.struct_time

so I suspect this bug has been lurking for some time.


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Comment By: Tim Peters (tim_one)
Date: 2001-12-26 22:06

Message:
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Boosted priority, assigned to Guido.

A stack fault is faster to produce via the one-liner

cPickle.dumps(time.localtime())

There's unbounded recursion.

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