Database Interaction GPYC Practice Questions (Page 1)

Questions 1–5

1. 1foundation · easy

   Which Python exception class is the base class for database-related errors in the DB-API 2.0 specification?

   • ARuntimeError
   • BDatabaseError
   • CIOError
   • DValueError
   Reveal Solution Discussion Select an answer first
2. 2foundation · easy

   In Python's sqlite3 module, which placeholder symbol is used in a parameterized query?

   • A@p
   • B%s
   • C?
   • D:name
   Reveal Solution Discussion Select an answer first
4. 3expert · hard

   A Python application uses SQLAlchemy ORM to query a large table. The application needs to export data to a CSV file, but loading all rows into memory causes out-of-memory errors. The developer must also ensure that the export does not block other database operations for too long. Which approach best addresses both concerns?

   • AUse fetchall() and write the entire result set to the CSV file at once.
   • BUse yield_per(1000) in the query to stream rows in batches and process each batch immediately.
   • CUse a subquery to limit the result set to 1000 rows and run the query multiple times.
   • DUse a server-side cursor with fetchmany() and hold the transaction open until all rows are processed.
   Reveal Solution Discussion Select an answer first
5. 4expert · hard

   A financial application processes a batch of transactions. Each transaction must be committed individually, but if a transaction fails, the application should retry it up to three times before giving up. The application must also ensure that a failed transaction does not affect previously committed ones. Which approach best meets these requirements?

   • AUse a savepoint before each transaction and roll back to the savepoint on failure.
   • BUse a single transaction for the entire batch and roll back on any failure.
   • CUse autocommit for each transaction and do not implement retries.
   • DUse a new transaction for each transaction, commit after each success, and retry the failed transaction up to three times before moving on.
   Reveal Solution Discussion Select an answer first
6. 5expert · hard

   A Python service connects to a PostgreSQL database and performs a series of INSERT and UPDATE operations. The service must be resilient to transient network failures, but it must not duplicate transactions if a failure occurs after the database commits but before the client receives the acknowledgment. Which strategy best handles this ambiguity?

   • AUse a unique constraint on all columns to prevent duplicate inserts.
   • BUse idempotent operations, such as upserts, so that retrying a transaction does not create duplicate records.
   • CCommit after every statement and rely on the database's transaction log to detect duplicates.
   • DAlways roll back and retry the entire transaction from the beginning.
   Reveal Solution Discussion Select an answer first