14.3 Pickling

The read and write methods you just saw convert data to strings before writing. Complex types (such as objects and classes) cannot be written this way. With Python's module pickle, you can save any object and also multiple objects to a file.

Data can be saved in plain-text (ASCII) format or using a slightly more efficient binary format. There are two main methods: dump, which saves a pickled representation of a Python object to a file, and load, which retrieves a pickled object from the file. The basic usage is like this:

import pickle
with open('file.dat','wb') as myfile:
    a = random.rand(20,20)
    b = 'hello world'
    pickle.dump(a,myfile)    # first call: first object
    pickle.dump(b,myfile)    # second call: second object

import pickle
with open('file.dat','rb') as myfile:
    numbers = pickle.load(myfile) # restores the array
    text = pickle.load(myfile)    # restores the string

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