freeCodeCamp/guide/english/python/pickling/index.md

title
Pickling in Python

Overview

Pickling refers to the serialization and deserialization of an object in Python. It essentially stores an object to a file so the user can load it later on. During pickling, the Python object is converted to a binary stream.

Usage Example

First let's create a class:

class ExampleClass():
  def __init__(self, integer, string, number_list):
    self.integer = integer
    self.string = string
    self.number_list = number_list
  def print_attributes(self):
    print(self.integer, self.string, self.number_list)
  def print_sum(self):
    print(sum(self.number_list))

instance = ExampleClass(10, 'rubberducky', [1, 2, 3, 1, 2])
instance.print_attributes() # Prints 10 rubberducky [1, 2, 3, 1, 2]
instance.print_sum() # Prints 9

Now, let's try pickling it:

import pickle
with open('file.pickle', 'wb') as file:
  pickle.dump(instance, file)

This creates the file file.pickle. According to this StackOverflow thread, Python 3's preferred extension is .pickle. Now we simply need to lead it:

import pickle
with open('file.pickle', 'rb') as file:
  loaded = pickle.load(file)
  loaded.print_attributes() # Prints 10 rubberducky [1, 2, 3, 1, 2]
  loaded.print_sum() # Prints 9

It works! Note that both times, open()'s mode was rb or wb, as opposed to the regular r or w (which stand for read and write). This is because of how pickle works: it uses binary.

More Information

Python - Pickling