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Name: [002] Ian Ozsvald
Member: 101 months
Authored: 181 videos
Description: I am the co-founder of ShowMeDo (see http://showmedo.com/about), author of `The Screencasting Handbook <http://thescreencastinghandbook.com>`_ and the founder of the professional screencast production company `ProCasts <http://procasts.co.uk>`_: .. image:: http://procasts.co.uk/media/procasts_sma ...

Serialising for persistence with cPickle [ID:1353] (5/5)

in series: Python Beginners - File I/O

(Showmedo is undergoing major changes. To report any problems viewing the videos please email us and include browser and OS specifics. Cheers - Kyran.)

cPickle lets us serialise our data very simply to a file. This means we can build up a datastore that is persistent between runs of our Python code and we don't need to write any parsers to load it back in - we just un-pickle it. To understand the limitations, see what can and can't be pickled.

"""cPickly allows us to quick store/retrieve structured data"""
import cPickle
# cPickle is the faster implementation of the standard pickle module

# http://docs.python.org/library/pickle.html
# Protocol version 0 is the original ASCII protocol and is backwards compatible with earlier versions of Python.
# Protocol version 1 is the old binary format which is also compatible with earlier versions of Python.
# Protocol version 2 was introduced in Python 2.3. It provides much more efficient pickling of new-style classes.

# what can be pickled?
# http://docs.python.org/library/pickle.html#what-can-be-pickled-and-unpickled

d = dict()
d['alice'] = 22
d['bob'] = 33

# we'll write using the original ASCII protocol 0
f0 = file('data_0.pickle', 'w')
cPickle.dump(d, f0, 0)
f0.close()

# protocol 2 requires binary files, it is much more space efficient
# note that protocols *aren't* compatible, you must stick to one and use it
#f2 = file('data_2.pickle', 'wb')
#cPickle.dump(d, f2, 2)
#f2.close()

# open the file for binary input
#f_in = file('data_2.pickle', 'rb')
# load the pickled object, the protocol is detected
#d_in = cPickle.load(f_in)
# print the unpickled object
#print d_in

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All comments excluding tick-boxed quick-comments

Great video! Very nice work. Thanks!


Helpful, knowing about the protocol will come in handy.


Great stuff, as usual.


Liked all the file i/o modules. Not sure the picture was useful -- the jury is out.


thank you, great work


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