How to use Pickle to save and load Variables in Python?

Serialization is a technique used to save the state of an object from any process. We can later use this state by deserialization, to continue the process. Pickle is a python module that makes it easy to serialize or save variables and load them when needed. Unlike JSON serialization, Pickle converts the object into a binary string. JSON is text specific, but Pickle is python specific, and it can serialize the custom classes which JSON fails to serialize. Due to this feature, it is heavily used in training machine learning models. This article discusses how variables can be saved and loaded in python using pickle.

Functions used:

• In python, dumps() method is used to save variables to a pickle file.

Syntax:

pickle.dumps(obj, protocol=None, *, fix_imports=True, buffer_callback=None)

• In python, loads() is used to load saved data from a pickled file

Syntax:

pickle.loads(data, /, *, fix_imports=True, encoding=”ASCII”, errors=”strict”, buffers=None)

Saving a variable:

• Method 1: Passing the variable

In dumps() method, we can pass the variable, and it will return us the binary string for the same. We can then transmit it to other python modules or save in a database.

Example:

Python3

import pickle

# Create a variable
myvar = [{'This': 'is', 'Example': 1}, 'of',
         'serialisation', ['using', 'pickle']]

# Use dumps() to make it serialized
serialized = pickle.dumps(myvar)

print(serialized)

Output:

b’\x80\x04\x95K\x00\x00\x00\x00\x00\x00\x00]\x94(}\x94(\x8c\x04This\x94\x8c\x02is\x94\x8c\x07Example\x94K\x01u\x8c\x02of\x94\x8c\rserialisation\x94]\x94(\x8c\x05using\x94\x8c\x06pickle\x94ee.’

• Method 2:  We can directly save the variable in a file itself.

Example:

Python3

import pickle

# Create a variable
myvar = [{'This': 'is', 'Example': 2}, 'of',
         'serialisation', ['using', 'pickle']]

# Open a file and use dump()
with open('file.pkl', 'wb') as file:

    # A new file will be created
    pickle.dump(myvar, file)

Loading a Variable:

• Method 1: 

The loads() method takes a binary string and returns the corresponding variable. If the string is invalid, it throws a PickleError.

Example:

Python3

import pickle

# This is the result of previous code
binary_string = b'\x80\x04\x95K\x00\x00\x00\x00\x00\x00\x00]\x94(}\x94(\x8c\x04This\x94\x8c\x02is\x94\x8c\x07Example\x94K\x01u\x8c\x02of\x94\x8c\rserialisation\x94]\x94(\x8c\x05using\x94\x8c\x06pickle\x94ee.'

# Use loads to load the variable
myvar = pickle.loads(binary_string)

print(myvar)

Output:

[{‘This’: ‘is’, ‘Example’: 1}, ‘of’, ‘serialisation’, [‘using’, ‘pickle’]]

• Method 2: 

The load() method loads a pickled file and returns a deserialized variable.

Example:

Python3

import pickle

# Open the file in binary mode
with open('file.pkl', 'rb') as file:

    # Call load method to deserialze
    myvar = pickle.load(file)

    print(myvar)

Output:

[{‘This’: ‘is’, ‘Example’: 2}, ‘of’, ‘serialisation’, [‘using’, ‘pickle’]]