Python: Essential Reference, Third Edition

Persistence

It’s often necessary to save and restore the contents of an object to a file. One approach to this problem is to write a pair of functions that read and write data from a file in a special format. An alternative approach is to use the pickle and shelve modules.

The pickle module serializes an object into a stream of bytes that can be written to a file. For example, the following code writes an object to a file:

import pickle
object = someObject()
f = open(filename,'w')
pickle.dump(object, f)      # Save object

To restore the object, you can use the following code:

import pickle
f = open(filename,'r')
object = pickle.load(f)   # Restore the object

The shelve module is similar, but saves objects in a dictionary-like database:

 import shelve ...