Bugs item #1724366, was opened at 2007-05-23 18:42
Message generated for change (Comment added) made by gjb1002
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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Geoffrey Bache (gjb1002)
Assigned to: Nobody/Anonymous (nobody)
Summary: cPickle module doesn't work with universal line endings
Initial Comment:
On UNIX, I cannot read pickle files created on Windows using the cPickle
module, even if I open the file with universal line endings.
It works fine with the pickle module but is of course slower (and I have to
read lots of them)
I attach a test case that pickles and unpickles an smptlib.SMTP object,
converting the file to DOS format in between. There is nothing special about
SMTP, you can use any object at all in a different module.
On my system (RHEL4 with Python 2.4.3) I get the following output:
portmoller : pickletest.py cPickle
unix2dos: converting file dump to DOS format ...
Traceback (most recent call last):
File "pickletest.py", line 14, in ?
print load(readFile)
ImportError: No module named smtplib
portmoller : pickletest.py pickle
unix2dos: converting file dump to DOS format ...
<smtplib.SMTP instance at 0xb7ea350c>
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>Comment By: Geoffrey Bache (gjb1002)
Date: 2007-05-25 19:24
Message:
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Yes, I'm sure Python is trying to import "smtplib\r".
For various reasons I need to use protocol 0: not least because I use the
pickle files as test data and it's much easier to administer a load of text
files than a load of binary files.
I will experiment with reading the files in binary mode on Monday and get
back to you. My current workaround is to do loads(file.read()) instead of
load(file) which I guess is a performance penalty. Any idea whether this is
likely to be slower than just using the pickle module? (I haven't tested
this)
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Comment By: Gabriel Genellina (gagenellina)
Date: 2007-05-25 12:29
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The culprit is cPickle.c; it takes certain shortcuts for read() and
readline() depending on which type of file you pass in.
For a true file object, it uses its own implementation for those two
methods, ignoring the file mode.
But it appears that there is NO WAY universal line endings could work if
the pickle contains any unicode object. The pickle format for Unicode
quotes any \n but *not* \r so the unpickler cannot determine, when it sees
a "\r", if it is a MAC end-of-line or an embedded "\r".
So, the only safe end-of-line character for a pickle using protocol 0 is
"\n", and that means that the file must be written in binary mode.
(This may also indicate that you cannot read unicode objects with embedded
\r in a MAC using protocol 0, but I don't have a MAC to test it).
So, until this is fixed (either the module or the documentation), one
should forget about universal line endings and write all pickle files as
binary. (This way ALL lines end in \n and it should work fine on all
platforms)
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Comment By: Gabriel Genellina (gagenellina)
Date: 2007-05-25 11:04
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I don't see any "Attach" button...
Just add these lines near the top of the test script:
original__import = __import__
def myimport(name, *args):
print "import",repr(name)
return original__import(name,*args)
#end myimport
__builtins__.__import__ = myimport
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Comment By: Gabriel Genellina (gagenellina)
Date: 2007-05-25 11:00
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Please try again with this modified version. I think you will see that
Python is trying to import "smtplib\r"
On Windows, trying to read a pickle file with MAC line endings gives a
different error:
cPickle.UnpicklingError: pickle data was truncated
It seems that cPickle support for protocol 0 is broken. If you can, try to
use the higher, binary, protocols, they don't have this problem. Even if
you must use protocol 0, opening the file always in binary mode should not
have this problem.
----------------------------------------------------------------------
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