The pickle module implements an algorithm for turning an arbitrary Python object into a series of bytes. This process is also called serializing the object. The byte stream representing the object can then be transmitted or stored, and later reconstructed to create a new object with the same characteristics.

Encoding and decoding Data in String



In [1]:

    
import pickle
import pprint

data = [{'a': 'A', 'b': 2, 'c': 3.0}]
print('DATA:', end=' ')
pprint.pprint(data)

data_string = pickle.dumps(data)
print('PICKLE: {!r}'.format(data_string))









    



DATA: [{'a': 'A', 'b': 2, 'c': 3.0}]
PICKLE: b'\x80\x03]q\x00}q\x01(X\x01\x00\x00\x00aq\x02X\x01\x00\x00\x00Aq\x03X\x01\x00\x00\x00bq\x04K\x02X\x01\x00\x00\x00cq\x05G@\x08\x00\x00\x00\x00\x00\x00ua.'



In [4]:

    
import pickle
import pprint

data1 = [{'a': 'A', 'b': 2, 'c': 3.0}]
print('BEFORE: ', end=' ')
pprint.pprint(data1)

data1_string = pickle.dumps(data1)
data2 = pickle.loads(data1_string)
print('AFTER : ', end=' ')
pprint.pprint(data2)

print('SAME? :', (data1 is data2))
print('EQUAL?:', (data1 == data2))









    



BEFORE:  [{'a': 'A', 'b': 2, 'c': 3.0}]
AFTER :  [{'a': 'A', 'b': 2, 'c': 3.0}]
SAME? : False
EQUAL?: True

Working with Stream



In [5]:

    
import io
import pickle
import pprint


class SimpleObject:

    def __init__(self, name):
        self.name = name
        self.name_backwards = name[::-1]
        return


data = []
data.append(SimpleObject('pickle'))
data.append(SimpleObject('preserve'))
data.append(SimpleObject('last'))

# Simulate a file.
out_s = io.BytesIO()

# Write to the stream
for o in data:
    print('WRITING : {} ({})'.format(o.name, o.name_backwards))
    pickle.dump(o, out_s)
    out_s.flush()

# Set up a read-able stream
in_s = io.BytesIO(out_s.getvalue())

# Read the data
while True:
    try:
        o = pickle.load(in_s)
    except EOFError:
        break
    else:
        print('READ    : {} ({})'.format(
            o.name, o.name_backwards))









    



WRITING : pickle (elkcip)
WRITING : preserve (evreserp)
WRITING : last (tsal)
READ    : pickle (elkcip)
READ    : preserve (evreserp)
READ    : last (tsal)

Problem with Reconstructing Objects



In [6]:

    
import pickle
import sys


class SimpleObject:

    def __init__(self, name):
        self.name = name
        l = list(name)
        l.reverse()
        self.name_backwards = ''.join(l)
data = []
data.append(SimpleObject('pickle'))
data.append(SimpleObject('preserve'))
data.append(SimpleObject('last'))

filename ='test.dat'

with open(filename, 'wb') as out_s:
    for o in data:
        print('WRITING: {} ({})'.format(
            o.name, o.name_backwards))
        pickle.dump(o, out_s)









    



WRITING: pickle (elkcip)
WRITING: preserve (evreserp)
WRITING: last (tsal)



In [7]:

    
with open(filename, 'rb') as in_s:
    while True:
        try:
            o = pickle.load(in_s)
        except EOFError:
            break
        else:
            print('READ: {} ({})'.format(
                o.name, o.name_backwards))









    



READ: pickle (elkcip)
READ: preserve (evreserp)
READ: last (tsal)