--- /dev/null
+# cursor.py - how to subclass the cursor type
+#
+# Copyright (C) 2004 Federico Di Gregorio <fog@debian.org>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by the
+# Free Software Foundation; either version 2, or (at your option) any later
+# version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY
+# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+# for more details.
+
+## put in DSN your DSN string
+
+DSN = 'dbname=test'
+
+## don't modify anything below this line (except for experimenting)
+
+import sys
+import psycopg2
+import psycopg2.extensions
+
+if len(sys.argv) > 1:
+ DSN = sys.argv[1]
+
+print "Opening connection using dsn:", DSN
+conn = psycopg2.connect(DSN)
+print "Encoding for this connection is", conn.encoding
+
+
+class NoDataError(psycopg2.ProgrammingError):
+ """Exception that will be raised by our cursor."""
+ pass
+
+class Cursor(psycopg2.extensions.cursor):
+ """A custom cursor."""
+
+ def fetchone(self):
+ """Like fetchone but raise an exception if no data is available.
+
+ Note that to have .fetchmany() and .fetchall() to raise the same
+ exception we'll have to override them too; even if internally psycopg
+ uses the same function to fetch rows, the code path from Python is
+ different.
+ """
+ d = psycopg2.extensions.cursor.fetchone(self)
+ if d is None:
+ raise NoDataError("no more data")
+ return d
+
+curs = conn.cursor(cursor_factory=Cursor)
+curs.execute("SELECT 1 AS foo")
+print "Result of fetchone():", curs.fetchone()
+
+# now let's raise the exception
+try:
+ curs.fetchone()
+except NoDataError, err:
+ print "Exception caugth:", err
+
+conn.rollback()