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What is pickling in Python

Understanding Pickling in Python

Imagine you have a delicious sandwich that you can't finish in one sitting, and you want to save it for later. You'd probably wrap it up and put it in the fridge. In programming, especially in Python, we sometimes need to save our data (like the sandwich) for later use. This is where the concept of pickling comes into play.

What is Pickling?

Pickling is the process of converting a Python object into a byte stream, a sequence of bytes that can be stored on disk or sent over a network. This byte stream can then be stored, and later on, retrieved and converted back into the original Python object. This process of converting back is called unpickling.

You can think of pickling as a way of packaging your data for transport or storage, much like how you might vacuum-seal food before freezing it. When you're ready to use the food again, you unseal and thaw it. With pickling, you're essentially vacuum-sealing your Python objects to be opened and used later.

Why Use Pickling?

Pickling is useful when you need to:

  • Save a program's state to disk so that you can continue running it later.
  • Send Python data over a network to another Python program.
  • Store Python objects in a database.

How to Pickle Objects in Python

To pickle an object in Python, you use the pickle module. Here's a simple example of how you can pickle a Python dictionary:

import pickle

# Let's create a simple dictionary.
my_data = {'key': 'value', 'number': 42}

# Now we'll pickle the dictionary.
with open('data.pkl', 'wb') as file:
    pickle.dump(my_data, file)

print("Data has been pickled.")

In this code:

  • We import the pickle module.
  • We create a dictionary called my_data.
  • We open a file called data.pkl in 'write binary' ('wb') mode.
  • We use pickle.dump(), which takes two arguments: the object we want to pickle and the file in which to store the pickled object.

The .pkl extension is a common convention for pickled files, but you can use any file extension you like.

Unpickling: How to Bring Your Data Back to Life

Once you've pickled your data and saved it to a file, you can retrieve it by unpickling. Here's how you do it:

import pickle

# Let's unpickle the dictionary we pickled earlier.
with open('data.pkl', 'rb') as file:
    my_data = pickle.load(file)

print("Data has been unpickled:")

In this code:

  • We open the data.pkl file in 'read binary' ('rb') mode.
  • We use pickle.load(), which reads the pickled object from the file and returns it.
  • We print out the unpickled data to confirm it's been retrieved successfully.

Pickling Without Files

Sometimes, you might want to pickle an object without immediately writing it to a file. Python allows you to do this by pickling to a bytes object:

import pickle

# Create an object.
my_list = [1, 2, 3, 'Python']

# Pickle to a bytes object.
pickled_list = pickle.dumps(my_list)

# Now `pickled_list` is a bytes object containing the pickled representation.

To unpickle from a bytes object, you use pickle.loads():

# Unpickle from a bytes object.
unpickled_list = pickle.loads(pickled_list)

# Check that we've got our original list back.

Safety Considerations

While pickling is powerful, it's important to remember that it can be unsafe to unpickle data from an untrusted source. Pickle files can be tampered with to include malicious code that could be executed during unpickling. Always ensure that the source of the pickle file is trusted before unpickling it.

Analogies to Help You Understand

To further help you understand, let's use some analogies:

Pickling as Packing for a Trip: Imagine you're packing your suitcase for a vacation. You carefully fold your clothes (organize your data) and place them in the suitcase (the pickle file). When you arrive at your destination (need the data again), you unpack (unpickle) your clothes.

Pickling as Time Capsules: Creating a pickle file is like burying a time capsule. You place objects inside (serialize your Python objects), seal it (write to a file), and dig it up in the future (unpickle) to remember the past (retrieve the objects).


In this blog post, we've unwrapped the concept of pickling in Python. It's a way to save your Python objects for later use, whether that's after a coffee break or when sending them to a friend's Python program across the world. Pickling is like a magical suitcase for your code's data, letting you pack and unpack objects as needed.

Just remember to handle this suitcase with care. Only unpack pickles from sources you trust, as a tampered pickle can cause more trouble than a spilled jar of pickles in your kitchen.

With the basics of pickling under your belt, you're now equipped to preserve your Python objects for the future, ensuring that not a byte of your hard work is ever lost. Happy coding, and may your data always stay fresh, no matter how long it's been pickled!