There is a strange behaviour in cPickle (in Python 2.2.1).
For big serialized file, the following:

        cPickle.loads(open("my_file").read())

can be much (e.g. 7 times) faster than:

        cPickle.load(open("my_file"))

It seems that cPickle use unbuffered reading or what ?
The pickle implementation doesn't have this behaviour,
and can even be
faster than the C one!

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I expect this has to do with extra overhead in Python to
read from the file, independent of buffering.  The cPickle
code is trying to read small numbers of bytes at a time. 
Each read used fread().  This is slow, because fread is slow
for small numbers of bytes.  It's also slow because cPickle
releases and acquires the global interpeter lock around the
fread() calls.

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Really no time to deal with this.