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Name: [002] Ian Ozsvald
Member: 128 months
Authored: 181 videos
Description: I am the co-founder of ShowMeDo (see, author of `The Screencasting Handbook <>`_ and the founder of the professional screencast production company `ProCasts <>`_: .. image:: ...

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

in series: Python Beginners - File I/O

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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

# 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?

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)

# 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)

# 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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Although as important as the software it supports, education and documentation are relatively neglected in the Open-source world. Coders love to code, and explaining how best to use or improve the software tends to be deferred or even sidelined.

At Showmedo we believe the community can play a vital role here and also say thanks for the tools and software that make our lives easier. If you have a piece of software you love or a programming langugage you are enthusiastic about, why not make a screencast showing others how to use it? All the stuff you wish you'd been told, the tips, tricks, insights that would have saved you time and frustration.

Screencasting is easier than you think, and we're happy to help you. You can emailus for advice or just use some of the how-to screencasts on the site. This screencasting learning-pathis a good place to start.

Kudos and Thanks for Ian

3 Minute Oveview (What Does Python Look Like?)

simple and informative. you draw me in
70 months ago


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