Transactions with Python sqlite3

Question

I\'m trying to port some code to Python that uses sqlite databases, and I\'m trying to get transactions to work, and I\'m getting really confused. I\'m really confused by th

Answer 1

Per the docs,

Connection objects can be used as context managers that automatically commit or rollback transactions. In the event of an exception, the transaction is rolled back; otherwise, the transaction is committed:

Therefore, if you let Python exit the with-statement when an exception occurs, the transaction will be rolled back.

import sqlite3

filename = '/tmp/test.db'
with sqlite3.connect(filename) as conn:
    cursor = conn.cursor()
    sqls = [
        'DROP TABLE IF EXISTS test',
        'CREATE TABLE test (i integer)',
        'INSERT INTO "test" VALUES(99)',]
    for sql in sqls:
        cursor.execute(sql)
try:
    with sqlite3.connect(filename) as conn:
        cursor = conn.cursor()
        sqls = [
            'update test set i = 1',
            'fnord',   # <-- trigger error
            'update test set i = 0',]
        for sql in sqls:
            cursor.execute(sql)
except sqlite3.OperationalError as err:
    print(err)
    # near "fnord": syntax error
with sqlite3.connect(filename) as conn:
    cursor = conn.cursor()
    cursor.execute('SELECT * FROM test')
    for row in cursor:
        print(row)
        # (99,)

yields

(99,)

as expected.