Consider:

>>> import pickle
>>> thing = open('foobar.txt','w')
>>> pickle.dumps(thing)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.6/pickle.py", line 1366, in dumps
    Pickler(file, protocol).dump(obj)
  File "/usr/lib/python2.6/pickle.py", line 224, in dump
    self.save(obj)
  File "/usr/lib/python2.6/pickle.py", line 306, in save
    rv = reduce(self.proto)
  File "/usr/lib/python2.6/copy_reg.py", line 70, in _reduce_ex
    raise TypeError, "can't pickle %s objects" % base.__name__
TypeError: can't pickle file objects

Seems entirely reasonable - of course I can't pickle an open file handle. But:

>>> pickle.dumps(thing, 2)
'\x80\x02c__builtin__\nfile\nq\x00)\x81q\x01.'
>>> pickle.loads(pickle.dumps(thing, 2))
<closed file '<uninitialized file>', mode '<uninitialized file>' at 0x7ff3c078>

Apparently I can pickle an open file, just not usefully.

Is this deliberate? It was obscuring a bug in my code, where I was wrongly pickling an object that owned a file. Under some conditions, that object also holds a pyodbc cursor, with the same result.

I don't see anything in PEP 307 about it. Was it just an oversight, or is there something important going on that I'm missing, that could let me get the exception I want even when pickling using protocol 2?

I'm using Python 2.6.5. I know, I know, but it's what comes with my distribution.

python pickle python-2.x
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