pickle - Python Object Serialization

Python object serialization and deserialization

The pickle module implements binary protocols for serializing and de-serializing Python objects.

Module Import

import pickle

Basic Operations

dumps() / loads() - Serialize to/from Bytes

import pickle

data = {'name': 'Alice', 'scores': [95, 87, 92]}

# Serialize to bytes
pickled = pickle.dumps(data)
print(pickled)  # b'\x80\x04\x95...'

# Deserialize from bytes
restored = pickle.loads(pickled)
print(restored)  # {'name': 'Alice', 'scores': [95, 87, 92]}

dump() / load() - Serialize to/from File

import pickle

data = {'name': 'Alice', 'age': 30}

# Write to file
with open('data.pkl', 'wb') as f:
    pickle.dump(data, f)

# Read from file
with open('data.pkl', 'rb') as f:
    restored = pickle.load(f)
print(restored)

Pickling Complex Objects

import pickle

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def __repr__(self):
        return f"Person('{self.name}', {self.age})"

# Pickle custom object
person = Person('Alice', 30)
pickled = pickle.dumps(person)

# Unpickle
restored = pickle.loads(pickled)
print(restored)  # Person('Alice', 30)

Protocol Versions

import pickle

data = {'key': 'value'}

# Use latest protocol (fastest)
pickled = pickle.dumps(data, protocol=pickle.HIGHEST_PROTOCOL)

# Use specific protocol
pickled = pickle.dumps(data, protocol=4)

Practical Examples

Cache Expensive Computation

import pickle
import os

def expensive_computation():
    # Simulate expensive operation
    return [i**2 for i in range(1000000)]

cache_file = 'cache.pkl'

if os.path.exists(cache_file):
    with open(cache_file, 'rb') as f:
        result = pickle.load(f)
    print("Loaded from cache")
else:
    result = expensive_computation()
    with open(cache_file, 'wb') as f:
        pickle.dump(result, f)
    print("Computed and cached")

Save Program State

import pickle

class GameState:
    def __init__(self):
        self.level = 1
        self.score = 0
        self.player_pos = (0, 0)
    
    def save(self, filename):
        with open(filename, 'wb') as f:
            pickle.dump(self, f)
    
    @staticmethod
    def load(filename):
        with open(filename, 'rb') as f:
            return pickle.load(f)

# Save game state
state = GameState()
state.level = 5
state.score = 1000
state.save('savegame.pkl')

# Load game state
restored = GameState.load('savegame.pkl')
print(f"Level: {restored.level}, Score: {restored.score}")

Security Warning: Never unpickle data from untrusted sources. Pickle can execute arbitrary code during unpickling.

For data interchange, prefer JSON. Use pickle only for trusted data and Python-to-Python communication.

json

JSON encoding/decoding

shelve

Python object persistence