Python · Theory

Transactions

Theory

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Transactions

Transactions is about talking to a database from Python. Pattern is always: connect → cursor → execute → fetch or commit → close.

For Transactions: use ? placeholders (or the driver’s params). Never build SQL with + user text — that is injection. sqlite3 is in the stdlib for practice; MySQL/Mongo need a driver.

Transactions on the board — insert Asha, select her back, print the name. Same idea on MySQL. Close the connection.

Transactions — output — committed 1. commit keeps the write; rollback undoes it.

Exam tip

Steps in order: connect → execute → fetch/commit → close. Mention placeholders.

Example

# Transactions
import sqlite3
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("create table t(n integer)")
try:
    cur.execute("insert into t values(1)")
    con.commit()
    print("committed", cur.execute("select n from t").fetchone()[0])
except Exception:
    con.rollback()
    print("rolled back")
con.close()

Transactions — output: committed 1. commit keeps the write; rollback undoes it.

Short notes

DefTransactions uses connect + cursor + SQL/API.
RuleTransactions — parameterized queries. Never + user text into SQL.
RememberTransactions — commit after write. close when done.
TrapTransactions — open connections left hanging; passwords in source.

# Transactions import sqlite3 con = sqlite3.connect(":memory:") cur = con.cursor() cur.execute("create table t(n integer)") try: cur.execute("insert into t values(1)") con.commit() print("committed", cur.execute("select n from t").fetchone()[0]) except Exception: con.rollback() print("rolled back") con.close()

Transactions

Example

Short notes

Questions

Transactions

Example

Short notes

Questions