pickle - Understanding Pickling in Python

Question

I have recently got an assignment where I need to put a dictionary (where each key refers to a list) in pickled form. The only problem is I have no idea what pickled form is. Could anyone point me in the right direction of some good resources to help me learn this concept?

Answer 1

The pickle module implements a fundamental, but powerful algorithm for serializing and de-serializing a Python object structure.

Pickling - is the process whereby a Python object hierarchy is converted into a byte stream, and Unpickling - is the inverse operation, whereby a byte stream is converted back into an object hierarchy.

Pickling (and unpickling) is alternatively known as serialization, marshalling, or flattening.

import pickle

data1 = {'a': [1, 2.0, 3, 4+6j],
         'b': ('string', u'Unicode string'),
         'c': None}

selfref_list = [1, 2, 3]
selfref_list.append(selfref_list)

output = open('data.pkl', 'wb')

# Pickle dictionary using protocol 0.
pickle.dump(data1, output)

# Pickle the list using the highest protocol available.
pickle.dump(selfref_list, output, -1)

output.close()

To read from a pickled file -

import pprint, pickle

pkl_file = open('data.pkl', 'rb')

data1 = pickle.load(pkl_file)
pprint.pprint(data1)

data2 = pickle.load(pkl_file)
pprint.pprint(data2)

pkl_file.close()

source - https://docs.python.org/2/library/pickle.html