Explain the concept of transaction isolation and its role in ensuring data integrity.

Transaction isolation is one of the key principles of transaction management in databases, which guarantees that concurrently executing transactions do not affect each other and do not lead to data inconsistency.

The role of isolation is to ensure data integrity when multiple users or processes access data simultaneously. Without isolation, issues such as:

• "Dirty read" — reading data that has been modified but not yet committed by another transaction;
• Non-repeatable read — when data changes between two reads within the same transaction;
• Phantom read — appearance of new rows that were not visible during the first read.

Isolation levels (e.g., Read Uncommitted, Read Committed, Repeatable Read, Serializable) allow balancing between performance and strict data integrity.

An example in Python using the sqlite3 library:

import sqlite3

conn = sqlite3.connect('example.db')
conn.isolation_level = 'DEFERRED'  # transaction isolation level
cursor = conn.cursor()

try:
    cursor.execute('BEGIN TRANSACTION')
    cursor.execute("UPDATE accounts SET balance = balance - 100 WHERE id = 1")
    cursor.execute("UPDATE accounts SET balance = balance + 100 WHERE id = 2")
    conn.commit()
except Exception as e:
    conn.rollback()
    print('Transaction error:', e)
finally:
    conn.close()

Here, isolation guarantees that changes in one transaction are not visible to others until it is completed, preventing inconsistency.