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# cursor.py - how to subclass the cursor type
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# Copyright (C) 2004 Federico Di Gregorio <fog@debian.org>
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by the
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# Free Software Foundation; either version 2, or (at your option) any later
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY
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# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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## put in DSN your DSN string
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## don't modify anything below this line (except for experimenting)
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import psycopg2.extensions
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print "Opening connection using dsn:", DSN
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conn = psycopg2.connect(DSN)
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print "Encoding for this connection is", conn.encoding
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class NoDataError(psycopg2.ProgrammingError):
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"""Exception that will be raised by our cursor."""
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class Cursor(psycopg2.extensions.cursor):
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"""A custom cursor."""
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"""Like fetchone but raise an exception if no data is available.
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Note that to have .fetchmany() and .fetchall() to raise the same
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exception we'll have to override them too; even if internally psycopg
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uses the same function to fetch rows, the code path from Python is
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d = psycopg2.extensions.cursor.fetchone(self)
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raise NoDataError("no more data")
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curs = conn.cursor(cursor_factory=Cursor)
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curs.execute("SELECT 1 AS foo")
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print "Result of fetchone():", curs.fetchone()
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# now let's raise the exception
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except NoDataError, err:
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print "Exception caugth:", err
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examples/cursor.py
