Alexandre Vassalotti added the comment:
There is no guarantee the binary representation of pickled data will be same
between different runs. We try to make it mostly consistent when we can, but
there are cases, like this one, where we cannot ensure consistency without
hurting performance
Serhiy Storchaka added the comment:
Here is a minimal reproducer. Results:
pickle.dumps('spam', 2)
0: \x80 PROTO 2
2: USHORT_BINSTRING 'spam'
8: qBINPUT 0
10: .STOP
highest protocol among opcodes = 2
pickle.dumps('spam1'[:-1], 2)
0: \x80 PROTO 2
Antoine Pitrou added the comment:
As soon as hash randomization is turned on (and it's the default starting with
Python 3.3), the pickled representation of dicts will also vary from run to run:
$ python -R -c import pickle; print pickle.dumps({'a':1, 'b':2}) |md5sum
Serhiy Storchaka added the comment:
It is surprising that the pickled representation of 1-element dict varies from
run to run.
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Ramchandra Apte added the comment:
Try `./python -R -c import pickle; print(pickle.dumps({'a':1, 'v':1}))
|md5sum`. The output will differ on subsequent run, while trying `./python -R
-c import pickle; print(pickle.dumps({'a':1})) |md5sum`, the output is always
the same. I suspect because the
Ramchandra Apte added the comment:
Darn, last sentence has some mistakes.
I suspect this issue is happening because the order of a dictionary is
different on every run (try repr).
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Ramchandra Apte added the comment:
Further proof:
here are the results of two invocations of `./python -R -c import pickle;
print(pickle.dumps({'a':1, 'v':1}))`
b'\x80\x03}q\x00(X\x01\x00\x00\x00vq\x01K\x01X\x01\x00\x00\x00aq\x02K\x01u.'
Serhiy Storchaka added the comment:
It is most probable that the difference is caused by the string interning.
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Changes by Serhiy Storchaka storch...@gmail.com:
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stage: - needs patch
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New submission from Philipp Mölders philipp.moeld...@googlemail.com:
I think there is a problem within cPickle. I wanted to store a dictionary with
only one entry with cPickle.dump() this works fine and can be loaded with
cPickle.load(). But if you store the loaded data with cPickle.dump()
Changes by Philipp Mölders philipp.moeld...@googlemail.com:
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type: - behavior
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R. David Murray rdmur...@bitdance.com added the comment:
If the load produces the same result, why does it matter that what is on disk
differs?
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Philipp Mölders philipp.moeld...@googlemail.com added the comment:
The file on disk matters for a replication service, so if a file is touched but
not changed it will not be replicated, but in this special case the data change
even when the structures have not changed. So if this happens very
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