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What is pickle in Python

Understanding Pickle in Python

When you're learning programming, it's like learning how to cook. You prepare different ingredients (data) to create a dish (a program). But what if you want to save your dish so you can enjoy it later, or share it with someone else? In the world of Python programming, we have a special tool for that called 'pickle'.

What is Pickling?

Imagine you have made a delicious soup (created some data) and you want to save it for later. In the kitchen, you might put it in a container and freeze it. In Python, the process of 'pickling' is similar. It's how you take an object in Python, like a list, dictionary, or even a custom object, and convert it into a character stream. This stream contains all the necessary information to reconstruct the object in another Python script or another point in time.

The concept is called serialization - turning structured data into a format that can be stored and then reconstructed later. Pickling is Python's own way of serializing objects.

Why Use Pickle?

You might wonder why we need to save objects like this. There are many reasons:

  • Saving progress: If your program takes a long time to run, you might want to save the results (data) so you can continue later without starting from scratch.
  • Sharing data: You can send this pickled data to someone else, and they can load it into their own Python environment.
  • Data persistence: If you have a web application, you might want to save user sessions or settings between visits.

How to Pickle Objects

Let's dive into the actual code. To use pickle, you first need to import the module:

import pickle

Imagine you have a list of fruits that you want to pickle. Here's how you would do it:

fruits = ['apple', 'banana', 'cherry']

# Open a file for writing binary data
with open('fruits.pkl', 'wb') as file:
    pickle.dump(fruits, file)

In this example, we've created a file called 'fruits.pkl' where we'll store our pickled list. The 'wb' stands for 'write binary', because the pickled data is binary, not text.

How to Unpickle Objects

Now, let's say we want to get our list of fruits back. This process is called 'unpickling' or 'deserialization'. Here's how you would do it:

# Open the file for reading binary data
with open('fruits.pkl', 'rb') as file:
    unpickled_fruits = pickle.load(file)

# Output: ['apple', 'banana', 'cherry']

We open the 'fruits.pkl' file in 'read binary' ('rb') mode and use pickle.load to read the pickled object back into memory.

Safety Considerations

It's important to note that pickling is not secure against erroneous or maliciously constructed data. Never unpickle data received from an untrusted or unauthenticated source.

Pickle Protocols

Pickle has different protocols which are methods that define how the serialization process happens. Each newer protocol adds improvements. You can specify the protocol version you want to use:

# Using a specific pickle protocol
with open('fruits.pkl', 'wb') as file:
    pickle.dump(fruits, file, protocol=pickle.HIGHEST_PROTOCOL)

The HIGHEST_PROTOCOL is the newest protocol available in your Python version.

Limitations and Alternatives

Pickle is great, but it's not perfect. It's specific to Python, which means you can't use pickled data with other programming languages. Also, it may not handle all data types and can be slow with large data sets.

For these reasons, you might consider alternatives like json for text-based serialization or numpy for numerical data arrays.

When Not to Use Pickle

  • Security-sensitive applications: If your data is sensitive, you might want to use a more secure method of serialization.
  • Interoperability: If you need to share data with programs written in other languages, use a more universal format like JSON or XML.


Pickle in Python is like a magical jar where you can store your data creations and bring them back to life whenever you need them. It is incredibly useful for saving the state of your program or sharing data between different parts of your code. However, it's essential to use it wisely, considering its limitations and security implications.

As you continue your journey in programming, remember that just like in cooking, the tools you use can make a big difference in the outcome. Pickle is one of the many tools in your Python kitchen that can help you preserve your data dishes in just the right way. Use it when it's appropriate, and always be mindful of the recipe (context) you're working in. Happy coding, and may your data always stay fresh and ready to use!