shelve Module

The shelve module provides persistent dictionary storage using DBM backend. It is simpler than databases for small data persistence needs, storing Python objects as pickled values.

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Basic Usage

Creating a Shelf

import shelve
import tempfile
import os

tmpdir = tempfile.mkdtemp()
shelf_path = os.path.join(tmpdir, 'myshelf')

with shelve.open(shelf_path) as shelf:
    shelf['key1'] = 'value1'
    shelf['key2'] = [1, 2, 3]
    shelf['key3'] = {'nested': 'dict'}

with shelve.open(shelf_path) as shelf:
    print(shelf['key1'])
    print(shelf['key2'])

for f in os.listdir(tmpdir):
    os.remove(os.path.join(tmpdir, f))
os.rmdir(tmpdir)

Output:

value1
[1, 2, 3]

Shelf Operations

Dictionary-like Interface

import shelve
import tempfile
import os

tmpdir = tempfile.mkdtemp()
shelf_path = os.path.join(tmpdir, 'test')

with shelve.open(shelf_path) as shelf:
    shelf['name'] = 'Alice'
    shelf['age'] = 30

    print(f"Keys: {list(shelf.keys())}")
    print(f"Values: {list(shelf.values())}")
    print(f"'name' in shelf: {'name' in shelf}")

for f in os.listdir(tmpdir):
    os.remove(os.path.join(tmpdir, f))
os.rmdir(tmpdir)

Output:

Keys: ['name', 'age']
Values: ['Alice', 30]
'name' in shelf: True

Mutable Objects

Updating Nested Data

import shelve
import tempfile
import os

tmpdir = tempfile.mkdtemp()
shelf_path = os.path.join(tmpdir, 'test')

with shelve.open(shelf_path) as shelf:
    shelf['data'] = {'count': 0}

with shelve.open(shelf_path) as shelf:
    data = shelf['data']
    data['count'] += 1
    shelf['data'] = data

with shelve.open(shelf_path) as shelf:
    print(f"Updated: {shelf['data']}")

for f in os.listdir(tmpdir):
    os.remove(os.path.join(tmpdir, f))
os.rmdir(tmpdir)

Output:

Updated: {'count': 1}

Practical Applications

Configuration Storage

import shelve
import tempfile
import os

tmpdir = tempfile.mkdtemp()
shelf_path = os.path.join(tmpdir, 'config')

with shelve.open(shelf_path) as config:
    config['theme'] = 'dark'
    config['language'] = 'en'

with shelve.open(shelf_path) as config:
    theme = config.get('theme', 'light')
    print(f"Theme: {theme}")

for f in os.listdir(tmpdir):
    os.remove(os.path.join(tmpdir, f))
os.rmdir(tmpdir)

Output:

Theme: dark