Read-only: unable to initialise shared memory

SQLITE_READONLY_CANTINIT (1288) is returned when a read-only connection is unable to initialise the WAL-mode shared memory (-shm file), because initialisation would require a write.

1. 1WAL-mode database opened read-only where -shm file does not yet exist.
2. 2First connection to a WAL database is read-only and cannot create -shm.

Read-only open of a WAL-mode database when -shm initialisation is needed.

import sqlite3
# Open WAL database read-only with no existing -shm:
conn = sqlite3.connect('file:wal.db?mode=ro', uri=True)
conn.execute('SELECT 1')  # may raise SQLITE_READONLY_CANTINIT

sqlite3.OperationalError: attempt to write a readonly database

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