Pickled objects in Python

The inventor of Python has given a catchy name to saving objects in files as "pickled objects".
I often use the cPickle module and one can get by using only two powerful functions load and dump in applications.

1. Save a named object to a pickle file.

import cPickle
a = "The quick brown fox"
b = "Hello world."
c = 123

D = { "a": a, "b": b}

Note that we create a dictionary containing the assigned names of the objects, and their corresponding values. An object is stored in external file and it is possible to recover their contents (seconds, minutes, hours, days, even years later)! Now here is the code for storing in the pickfile.

pickfilename = "tmp.pck"
pickfile = open(pickfilename,"w")

cPickle.dump(D, pickfile)


The cPickle.dump() function expects an object and an open file in write mode. If you dump the contents of tmp.pck you will get something like this displayed on the screen:


The idea of using a dictionary is the most natural way of saving a set of variables you are interested at to save and look for values later. Of course if you only wanted to save the variable a, you can do cPickle.dump(a, pickfile)

The name of all active local variables can be accessed by the function vars() which is a dictionary. But it also includes loaded modules which you may not want to be included!

2. Load saved object in pickle file

Nowt that you have created a pickfile, "tmp.pck", let us take a look at it. Dumping it on the console gives

(dp1
S'a'
S'The quick brown fox'
p2
sS'b'
S'Hello world.'
p3

So at least we are at ease that the values are indeed stored for later access.

myvars = cPickel.load(open(pickilename,"r"))

We knew that the name of the dictionary variable stored was "D". But you dont have to use D.
Instead above, we use a new label, myvars.

Now we can recover the values of the former variables by indexing using 'a' and 'b' as keys.Thus,


a = myvars["a"]
b = myvars["b"]


Notes.

The cPickle functions has an additional parameter calle 'protocol'. At this point in time, we refer the interested reader to the Python
tutorial on the Pickle and cPickle modules.