Pickle compatibility between Python 2.7 and python 3.2

Jesus Cea jcea at jcea.es
Tue Feb 22 00:27:02 CET 2011


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I have 10MB pickled structure generated in Python 2.7. I only use basic
types (no clases) like sets, dictionaries, lists, strings, etc.

The pickle stores a lot of strings. Some of them should be "bytes",
while other should be "unicode". My idea is to import ALL the strings as
bytes in Python 3.2 and navigate the data structure to convert the
appropiate values to unicode, in a one-time operation (I version the
structure, so I can know if this conversion is already done, simply
storing a new version value).

But I get this error:

"""
Python 3.2 (r32:88445, Feb 21 2011, 13:34:07)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> f=open("file.pickle", mode="rb").read()
>>> len(f)
9847316
>>> b=pickle.loads(f,encoding="latin1")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: operation forbidden on released memoryview object
"""

I use the encoding "latin1" for transparent byte/unicode conversion (do
not touch the values!).

This seems to be a bug in Python 3.2. Any suggestion?.

PS: The bytestream is protocol 2.

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