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# cursor.py - how to subclass the cursor type
#
# Copyright (C) 2004-2010 Federico Di Gregorio <fog@debian.org>
#
# psycopg2 is free software: you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# psycopg2 is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser 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()
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