Python · Theory

DB connection

Theory

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DB connection

A database connection is the live link from Python to the database. Flow: connect → cursor → execute SQL → fetch or commit → close. Use ? placeholders (or the driver’s params). Never build SQL with + user text — that is injection. Commit after writes if autocommit is off. Close so connections don’t leak. Don’t put passwords in source.

Same pattern on sqlite3, MySQL driver, others. Viva steps in order. Mention placeholders in the same breath as execute.

DB connection — output — 1. ? placeholders — real parameterized query, not string + id.

Exam tip

Never string-format user text into SQL.

Example

# DB connection
import sqlite3
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("create table users(id integer)")
cur.execute("insert into users values(?)", (1,))
print(cur.execute("select id from users where id=?", (1,)).fetchone()[0])
con.close()

DB connection — output: 1. ? placeholders — real parameterized query, not string + id.

Short notes

Defconnect → cursor → execute → close.
RuleParameterized SQL.
TrapPasswords in source. Open connections.

# DB connection import sqlite3 con = sqlite3.connect(":memory:") cur = con.cursor() cur.execute("create table users(id integer)") cur.execute("insert into users values(?)", (1,)) print(cur.execute("select id from users where id=?", (1,)).fetchone()[0]) con.close()

DB connection

Example

Short notes

Questions

DB connection

Example

Short notes

Questions