What are Pickling and Unpickling in Python?

To serialize and de-serialize a Python object structure, we have the Pickle module in Python. The pickle module implements binary protocols for serializing and de-serializing a Python object structure.

Pickling is the process through which a Python object hierarchy is converted into a byte stream. To serialize an object hierarchy, you simply call the dumps() function.

Unpickling is the inverse operation. A byte stream from a binary file or bytes-like object is converted back into an object hierarchy. To de-serialize a data stream, you call the loads() function.

Pickling and unpickling are alternatively known as serialization.

What can be pickled and unpickled?

In Python, the following types can be pickled ?

• None, True, and False.
• integers, floating-point numbers, complex numbers.
• strings, bytes, bytearrays.
• tuples, lists, sets, and dictionaries containing only picklable objects.
• functions, built-in and user-defined.

Pickle Module Constants

The following are the constants provided by the pickle module ?

• pickle.HIGHEST_PROTOCOL ? The highest protocol version available. Integer value.

• pickle.DEFAULT_PROTOCOL ? The default protocol version used for pickling. Integer value. Currently the default protocol is 4

Pickle Module Functions

The following are the functions provided by the pickle module ?

• pickle.dump() ? Write the pickled representation of the object to the open file object file.

• pickle.dumps() ? Return the pickled representation of the object as a bytes object, instead of writing it to a file.

• pickle.load() ? Read the pickled representation of an object from the open file object file.

• pickle.loads() ? Return the reconstituted object hierarchy of the pickled representation data of an object

Example

First, the pickle module is imported ?

import pickle

We have created the following input to be pickled.

my_data = { 'BMW', 'Audi', 'Toyota', 'Benz'}

The demo.pickle file is created. This same .pickle file is pickled with the above list

with open("demo.pickle","wb") as file_handle:
   pickle.dump(my_data, file_handle, pickle.HIGHEST_PROTOCOL)

Now, unpickle the above pickled file and get the input values back.

with open("demo.pickle","rb") as file_handle:
   res = pickle.load(file_handle)
   print(res_data)

Let us now see the complete example

import pickle

# Input Data
my_data = { 'BMW', 'Audi', 'Toyota', 'Benz'}

# Pickle the input
with open("demo.pickle","wb") as file_handle:
   pickle.dump(my_data, file_handle, pickle.HIGHEST_PROTOCOL)

# Unpickle the above pickled file
with open("demo.pickle","rb") as file_handle:
   res = pickle.load(file_handle)
   print(my_data) # display the output

Output

{'Benz', 'Toyota', 'Audi', 'BMW'}