The DBMS OPPE psycopg2 Question: Nailing the Python–PostgreSQL Task

The DBMS OPPE has a rule that catches people out: alongside scoring at least ~35% overall, you must answer the Python-to-PostgreSQL connectivity question correctly to receive a final grade. It comes from Week 7, it uses psycopg2, and it is very learnable once you've written the pattern a few times.

The pattern you must know cold

Connect, get a cursor, run a parameterised query, fetch, and print exactly what's asked:

import psycopg2

conn = psycopg2.connect(dbname="...", user="...", password="...", host="...")
cur = conn.cursor()
cur.execute("SELECT name FROM students WHERE dept = %s", (dept,))
for row in cur.fetchall():
    print(row[0])

cur.close()
conn.close()

Note the %s placeholder with a tuple of parameters — that's parameterised querying, and it's how the course expects you to pass values safely.

Common mistakes on this question

• String-formatting the query (f"... {dept}") instead of using %s placeholders.
• Passing a single parameter as (dept) instead of the one-tuple (dept,) — without the comma it isn't a tuple.
• Reading cur.fetchall() as full rows but printing the whole tuple row instead of the column row[0].
• Forgetting to commit() after an INSERT/UPDATE (SELECT-only questions don't need it, but write ones do).
• Output formatting — printing extra spaces, wrong order, or the wrong columns.

How to practise it

Write the connect-cursor-execute-fetch loop from memory until it's automatic, then vary it: a filter, a join fed into Python, an aggregate. Reinforce the SQL itself on the DBMS practice set and your Python on the Python practice track. For the driver's exact API, keep the psycopg documentation handy.

FAQ

Is the psycopg2 question really mandatory? Yes — per the official grading rule, you must answer the Python-database-connectivity question correctly to get a final grade.

Do I need to commit after a SELECT? No. commit() is only needed after statements that change data (INSERT, UPDATE, DELETE).

Which week is it from? Week 7, Application Development. See the DBMS course page.