Saving a Python dict to a file using pickle

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Per Programming Python, 3rd Edition, there are a number of methods to store persistent data with Python:

  • I often use flat files to read or write text (string) data using the os library.
  • Flat files are read sequentially, but dbm files allow for keyed access to string data
  • The pickle module can be used to store non-string Python data structures, such as Python dicts. However, the data is not keyed as with dbm files.
  • shelve files combine the best of the dbm and pickle methods by storing pickled objects in dbm keyed files.
  • I've read good things about the ZODB object-oriented database , but I don't know too much about it. Per the book, it is a more powerful alternative to shelves.
  • The final option is interfacing with a full-fledged SQL relational databases. As I mentioned before, Python 2.5 has an interface to SQLite as part of the standard distribution.

Here is an example using pickle which writes a Python dict to a file and reads it back again:

import pickle

# write python dict to a file
mydict = {'a': 1, 'b': 2, 'c': 3}
output = open('myfile.pkl', 'wb')
pickle.dump(mydict, output)

# read python dict back from the file
pkl_file = open('myfile.pkl', 'rb')
mydict2 = pickle.load(pkl_file)

print mydict
print mydict2

{'a': 1, 'c': 3, 'b': 2}
{'a': 1, 'c': 3, 'b': 2}

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