Tell about the levels of transaction isolation.

Transaction isolation levels determine how and when the changes made by one transaction become visible to other transactions. The main isolation levels are:

• Read Uncommitted — the lowest level of isolation. A transaction can see changes made by other transactions even if they haven't been committed yet (dirty reads).

• Read Committed — a transaction only sees committed changes. It prevents dirty reads but allows non-repeatable reads.

• Repeatable Read — a transaction sees the same data during repeated reads, preventing non-repeatable reads. However, phantom reads can still occur.

• Serializable — the strictest level. Transactions are executed as if they were sequential, fully preventing phantom reads and ensuring maximum data integrity.

In Python, when working with databases via ORM or drivers, the isolation level can be set through connection or transaction parameters, for example:

conn = psycopg2.connect(...)
conn.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE)