source: people/peter.buschman/backup_monitoring/dal/dbapi/_dbapi.py@ 1150

###
### DAL DBAPI 2.0 Wrapper Module
###
### --PLB 2007-11-03
###

import types
import dtuple
import string

##
## Version Information
##
version_info = (1, 0, 0)
version = string.join(['%d' % (v) for v in version_info], '.')


##
## Return a wrapped DBAPI 2.0 module
##
##     The driver parameter may be an existing module object or the name of a module to be imported
##
def wrap(driver):
    return Module(driver)


#
# DBAPI Exceptions
#
# Thanks to Kevin Jacob's 'Virtual Exceptions'
# http://mail.python.org/pipermail/db-sig/2003-April/003345.html

#
# Warning
#
#     Exception raised for important warnings like data
#     truncations while inserting, etc. It must be a subclass of
#     the Python StandardError (defined in the module
#     exceptions).
#
class Warning(StandardError):
    pass

#
# Error
#
#     Exception that is the base class of all other error
#     exceptions. You can use this to catch all errors with one
#     single 'except' statement. Warnings are not considered
#     errors and thus should not use this class as base. It must
#     be a subclass of the Python StandardError (defined in the
#     module exceptions).
#
class Error(StandardError):
    pass

#
# InterfaceError
#
#     Exception raised for errors that are related to the
#     database interface rather than the database itself.  It
#     must be a subclass of Error.
#
class InterfaceError(Error):
    pass

#
# DatabaseError
#
#     Exception raised for errors that are related to the
#     database.  It must be a subclass of Error.
#
class DatabaseError(Error):
    pass

#
# DataError
#
#     Exception raised for errors that are due to problems with
#     the processed data like division by zero, numeric value
#     out of range, etc. It must be a subclass of DatabaseError.
#
class DataError(DatabaseError):
    pass

#
# OperationalError
#
#     Exception raised for errors that are related to the
#     database's operation and not necessarily under the control
#     of the programmer, e.g. an unexpected disconnect occurs,
#     the data source name is not found, a transaction could not
#     be processed, a memory allocation error occurred during
#     processing, etc.  It must be a subclass of DatabaseError.
#
class OperationalError(DatabaseError):
    pass

#
# IntegrityError
#
#     Exception raised when the relational integrity of the
#     database is affected, e.g. a foreign key check fails.  It
#     must be a subclass of DatabaseError.
#
class IntegrityError(DatabaseError):
    pass

#
# InternalError
#
#     Exception raised when the database encounters an internal
#     error, e.g. the cursor is not valid anymore, the
#     transaction is out of sync, etc.  It must be a subclass of
#     DatabaseError.
#
class InternalError(DatabaseError):
    pass

#
# ProgrammingError
#
#      Exception raised for programming errors, e.g. table not
#      found or already exists, syntax error in the SQL
#      statement, wrong number of parameters specified, etc.  It
#      must be a subclass of DatabaseError.
#
class ProgrammingError(DatabaseError):
    pass

#
# NotSupportedError
#
#     Exception raised in case a method or database API was used
#     which is not supported by the database, e.g. requesting a
#     .rollback() on a connection that does not support
#     transaction or has transactions turned off.  It must be a
#     subclass of DatabaseError.
#
class NotSupportedError(DatabaseError):
    pass


##
## DBAPI 2.0 Wrapper
##
class Module(object):

    #
    # BEGIN INIT
    #
    def __init__(self, driver):

        """DBAPI 2.0 Module Wrapper"""

        object.__init__(self)

        #
        # Set version
        #
        self.version_info = version_info
        self.version = version

        #
        # Act appropriately if driver is a module or a string (the name of a module)
        #
        if type(driver) is types.ModuleType:
            self.driver = driver
        elif type(driver) is str:
            self.driver = __import__(driver)
        else:
            raise ImportError, 'Could not import DBAPI module %s' % (driver)

        #
        # These module globals must be defined:
        #

        #
        # apilevel
        #
        #     String constant stating the supported DB API level.
        #     Currently only the strings '1.0' and '2.0' are allowed.
        #
        #     If not given, a DB-API 1.0 level interface should be
        #     assumed.
        #
        self.apilevel = '2.0'

        #
        # threadsafety
        #
        #     Integer constant stating the level of thread safety the
        #     interface supports. Possible values are:
        #
        #         0     Threads may not share the module.
        #         1     Threads may share the module, but not connections.
        #         2     Threads may share the module and connections.
        #         3     Threads may share the module, connections and
        #               cursors.
        #
        self.threadsafety = self.driver.threadsafety

        #
        # paramstyle
        #
        #     String constant stating the type of parameter marker
        #     formatting expected by the interface. Possible values are
        #     [2]:
        #
        #         'qmark'         Question mark style,
        #                         e.g. '...WHERE name=?'
        #         'numeric'       Numeric, positional style,
        #                         e.g. '...WHERE name=:1'
        #         'named'         Named style,
        #                         e.g. '...WHERE name=:name'
        #         'format'        ANSI C printf format codes,
        #                         e.g. '...WHERE name=%s'
        #         'pyformat'      Python extended format codes,
        #                         e.g. '...WHERE name=%(name)s'
        #
        self.paramstyle = self.driver.paramstyle

        #
        # This is the exception inheritance layout:
        #
        # StandardError
        # |__Warning
        # |__Error
        #    |__InterfaceError
        #    |__DatabaseError
        #       |__DataError
        #       |__OperationalError
        #       |__IntegrityError
        #       |__InternalError
        #       |__ProgrammingError
        #       |__NotSupportedError
        #
        # Note: The values of these exceptions are not defined. They should
        #       give the user a fairly good idea of what went wrong, though.
        #
        self.exceptions = [
            'Warning',
            'Error',
            'InterfaceError',
            'DatabaseError',
            'DataError',
            'OperationalError',
            'IntegrityError',
            'InternalError',
            'ProgrammingError',
            'NotSupportedError',
        ]

        #
        # Wrap captive driver exceptions
        #
        for exception in self.exceptions:

            driver_exception = getattr(self.driver, exception)

            if driver_exception:
                setattr(self, exception, driver_exception)

        #
        # STRING
        #
        #     This type object is used to describe columns in a database
        #     that are string-based (e.g. CHAR).
        #
        if hasattr(self.driver, 'STRING'):
            self.STRING = self.driver.STRING

        #
        # BINARY
        #
        #     This type object is used to describe (long) binary columns
        #     in a database (e.g. LONG, RAW, BLOBs).
        #
        if hasattr(self.driver, 'BINARY'):
            self.BINARY = self.driver.BINARY

        #
        # NUMBER
        #
        #     This type object is used to describe numeric columns in a
        #     database.
        #
        if hasattr(self.driver, 'NUMBER'):
            self.NUMBER = self.driver.NUMBER

        #
        # DATETIME
        #
        #     This type object is used to describe date/time columns in
        #     a database.
        #
        if hasattr(self.driver, 'DATETIME'):
            self.DATETIME = self.driver.DATETIME

        #
        # ROWID
        #
        #     This type object is used to describe the "Row ID" column
        #     in a database.
        #
        if hasattr(self.driver, 'ROWID'):
            self.ROWID = self.driver.ROWID

    #
    # END INIT
    #

    #
    # Access to the database is made available through connection
    # objects. The module must provide the following constructor for
    # these:
    #
    #     connect(parameters...)
    #
    #         Constructor for creating a connection to the database.
    #         Returns a Connection Object. It takes a number of
    #         parameters which are database dependent. [1]
    #
    def connect(self, *args, **kwargs):

        conn = self.driver.connect(*args, **kwargs)
        conn = Connection(conn, module=self)

        #
        # Optional DBAPI Extension
        #
        # Connection Attributes .Error, .ProgrammingError, etc.
        #
        #     All exception classes defined by the DB API standard should be
        #     exposed on the Connection objects are attributes (in addition
        #     to being available at module scope).
        #
        #     These attributes simplify error handling in multi-connection
        #     environments.
        #
        #     Warning Message: "DB-API extension connection.<exception> used"
        #
        for exception in self.exceptions:

            driver_exception = getattr(self, exception)

            if driver_exception:
                setattr(conn, exception, driver_exception)

        return conn

    #
    # The module exports the following constructors and singletons:
    #

    #
    # Date(year,month,day)
    #
    #     This function constructs an object holding a date value.
    #
    def Date(self, year, month, day):
        return self.driver.Date(year, month, day)

    #
    # Time(hour,minute,second)
    #
    #     This function constructs an object holding a time value.
    #
    def Time(self, hour, minute, second):
        return self.driver.Time(hour, minute, second)

    #  Timestamp(year,month,day,hour,minute,second)
    #
    #     This function constructs an object holding a time stamp
    #     value.
    #
    def Timestamp(self, year, month, day, hour, minute, second):
        return self.driver.Timestamp(year, month, day, hour, minute, second)

    #
    # DateFromTicks(ticks)
    #
    #     This function constructs an object holding a date value
    #     from the given ticks value (number of seconds since the
    #     epoch; see the documentation of the standard Python time
    #     module for details).
    #
    def DateFromTicks(self, ticks):
        return self.driver.DateFromTicks(ticks)

    #
    # TimeFromTicks(ticks)
    #
    #     This function constructs an object holding a time value
    #     from the given ticks value (number of seconds since the
    #     epoch; see the documentation of the standard Python time
    #     module for details).
    #
    def TimeFromTicks(self, ticks):
        return self.driver.TimeFromTicks(ticks)

    #
    # TimestampFromTicks(ticks)
    #
    #     This function constructs an object holding a time stamp
    #     value from the given ticks value (number of seconds since
    #     the epoch; see the documentation of the standard Python
    #     time module for details).
    #
    def TimestampFromTicks(self, ticks):
        return self.driver.TimestampFromTicks(ticks)

    #
    # Binary(string)
    #
    #     This function constructs an object capable of holding a
    #     binary (long) string value.
    #
    def Binary(self, string):
        return self.driver.Binary(string)

    #
    # SQL NULL values are represented by the Python None singleton on
    # input and output.
    #
    #
    # Note: Usage of Unix ticks for database interfacing can cause
    # troubles because of the limited date range they cover.
    #


##
## Connection Objects
##
class Connection(object):

    """DBAPI 2.0 Connection Wrapper"""

    def __init__(self, conn, module=None, paramstyle=None):

        object.__init__(self)

        self.conn = conn

        #
        # Set module and driver
        #
        if module is not None:

            self.module = module

            if hasattr(module, 'driver'):
                self.driver = module.driver
            else:
                self.driver = None

        else:

            self.module = None
            self.driver = None

        #
        # Set paramstyle
        #
        if paramstyle is not None:
            self.paramstyle = paramstyle
        elif self.driver is not None:
            self.paramstyle = self.driver.paramstyle

    #
    # Connection Objects should respond to the following methods:
    #

    #
    # .close()
    #
    #     Close the connection now (rather than whenever __del__ is
    #     called).  The connection will be unusable from this point
    #     forward; an Error (or subclass) exception will be raised
    #     if any operation is attempted with the connection. The
    #     same applies to all cursor objects trying to use the
    #     connection.  Note that closing a connection without
    #     committing the changes first will cause an implicit
    #     rollback to be performed.
    #
    def close(self):
        return self.conn.close()

    #
    # .commit()
    #
    #     Commit any pending transaction to the database. Note that
    #     if the database supports an auto-commit feature, this must
    #     be initially off. An interface method may be provided to
    #     turn it back on.
    #
    #     Database modules that do not support transactions should
    #     implement this method with void functionality.
    #
    def commit(self):
        return self.conn.commit()

    #
    # .rollback()
    #
    #     This method is optional since not all databases provide
    #     transaction support. [3]
    #
    #     In case a database does provide transactions this method
    #     causes the the database to roll back to the start of any
    #     pending transaction.  Closing a connection without
    #     committing the changes first will cause an implicit
    #     rollback to be performed.
    def rollback(self):
        return self.conn.rollback()

    #
    # .cursor()
    #
    #     Return a new Cursor Object using the connection.  If the
    #     database does not provide a direct cursor concept, the
    #     module will have to emulate cursors using other means to
    #     the extent needed by this specification.  [4]
    #
    def cursor(self):
        curs = self.conn.cursor()
        return Cursor(curs, conn=self, paramstyle=self.paramstyle)  # include self so the optional .connection attribute can be set properly

    #
    # Optional DBAPI Extension
    #
    # Connection Attribute .messages
    #
    #     Same as cursor.messages except that the messages in the list
    #     are connection oriented.
    #
    #     The list is cleared automatically by all standard connection
    #     methods calls (prior to executing the call) to avoid excessive
    #     memory usage and can also be cleared by executing "del
    #     connection.messages[:]".
    #
    #     Warning Message: "DB-API extension connection.messages used"
    #
    # NOT CURRENTLY IMPLEMENTED
    #

##
## Cursor Objects
##
##     These objects represent a database cursor, which is used to
##     manage the context of a fetch operation. Cursors created from
##     the same connection are not isolated, i.e., any changes
##     done to the database by a cursor are immediately visible by the
##     other cursors. Cursors created from different connections can
##     or can not be isolated, depending on how the transaction support
##     is implemented (see also the connection's rollback() and commit()
##     methods.)
##
class Cursor(object):

    def __init__(self, curs, conn, paramstyle=None):

        object.__init__(self)

        self.cursor = curs
        self.curs = curs

        #
        # Set module and driver
        #
        if conn.module is not None:

            self.module = conn.module

            if hasattr(conn.module, 'driver'):
                self.driver = conn.module.driver
            else:
                self.driver = None

        else:

            self.module = None
            self.driver = None

        #
        # Set paramstyle
        #
        if paramstyle is not None:
            self.paramstyle = paramstyle
        elif self.driver is not None:
            self.paramstyle = self.driver.paramstyle

        #
        # Optional DBAPI Extension
        #
        # Cursor Attributes .connection
        #
        #     This read-only attribute return a reference to the Connection
        #     object on which the cursor was created.
        #
        #     The attribute simplifies writing polymorph code in
        #     multi-connection environments.
        #
        #     Warning Message: "DB-API extension cursor.connection used"
        #
        self.connection = conn
        self.conn = conn

        #
        # Add convenience commit method
        #
        self.commit = self.conn.commit

    #
    # Cursor Objects should respond to the following methods and attributes:
    #

    #
    # .description
    #
    #     This read-only attribute is a sequence of 7-item
    #     sequences.  Each of these sequences contains information
    #     describing one result column: (name, type_code,
    #     display_size, internal_size, precision, scale,
    #     null_ok). The first two items (name and type_code) are
    #     mandatory, the other five are optional and must be set to
    #     None if meaningfull values are not provided.
    #
    #     This attribute will be None for operations that
    #     do not return rows or if the cursor has not had an
    #     operation invoked via the executeXXX() method yet.
    #
    #     The type_code can be interpreted by comparing it to the
    #     Type Objects specified in the section below.
    #
    description = property(lambda self: self.curs.description)

    #
    # Update column descriptions for dtuple (not part of DBAPI)
    #
    def update_columns(self):

        if self.curs.description:

            columns = []

            for d in self.curs.description:
                column = d[0]
                columns.append(d[0])

            self.columns = dtuple.TupleDescriptor([[column] for column in columns])

    #
    # .rowcount
    #
    #     This read-only attribute specifies the number of rows that
    #     the last executeXXX() produced (for DQL statements like
    #     'select') or affected (for DML statements like 'update' or
    #     'insert').
    #
    #     The attribute is -1 in case no executeXXX() has been
    #     performed on the cursor or the rowcount of the last
    #     operation is not determinable by the interface. [7]
    #
    #     Note: Future versions of the DB API specification could
    #     redefine the latter case to have the object return None
    #     instead of -1.
    #
    rowcount = property(lambda self: self.curs.rowcount)

    #
    # .callproc(procname[,parameters])
    #
    #     (This method is optional since not all databases provide
    #     stored procedures. [3])
    #
    #     Call a stored database procedure with the given name. The
    #     sequence of parameters must contain one entry for each
    #     argument that the procedure expects. The result of the
    #     call is returned as modified copy of the input
    #     sequence. Input parameters are left untouched, output and
    #     input/output parameters replaced with possibly new values.
    #
    #     The procedure may also provide a result set as
    #     output. This must then be made available through the
    #     standard fetchXXX() methods.
    #
    def callproc(self, procname, parameters=[], *args, **kwargs):

        #
        # Call the wrapped method and save the results
        #
        results = self.curs.callproc(procname, parameters, *args, **kwargs)

        #
        # Update the column descriptions for dtuple
        #
        self.update_columns()

        #
        # Return the saved results
        #
        return results

    #
    # .close()
    #
    #     Close the cursor now (rather than whenever __del__ is
    #     called).  The cursor will be unusable from this point
    #     forward; an Error (or subclass) exception will be raised
    #     if any operation is attempted with the cursor.
    #
    def close(self, *args, **kwargs):
        return self.curs.close(*args, **kwargs)

    #
    # .execute(operation[,parameters])
    #
    #     Prepare and execute a database operation (query or
    #     command).  Parameters may be provided as sequence or
    #     mapping and will be bound to variables in the operation.
    #     Variables are specified in a database-specific notation
    #     (see the module's paramstyle attribute for details). [5]
    #
    #     A reference to the operation will be retained by the
    #     cursor.  If the same operation object is passed in again,
    #     then the cursor can optimize its behavior.  This is most
    #     effective for algorithms where the same operation is used,
    #     but different parameters are bound to it (many times).
    #
    #     For maximum efficiency when reusing an operation, it is
    #     best to use the setinputsizes() method to specify the
    #     parameter types and sizes ahead of time.  It is legal for
    #     a parameter to not match the predefined information; the
    #     implementation should compensate, possibly with a loss of
    #     efficiency.
    #
    #     The parameters may also be specified as list of tuples to
    #     e.g. insert multiple rows in a single operation, but this
    #     kind of usage is depreciated: executemany() should be used
    #     instead.
    #
    #     Return values are not defined.
    #
    def execute(self, operation, parameters=None, *args, **kwargs):

        #
        # Set appropriate default parameters depending on paramstyle type
        #
        if not parameters:
            if self.paramstyle in ['qmark', 'numeric', 'format']:
                #
                # sequence
                #
                parameters = []
            else:
                #
                # mapping
                #
                parameters = {}

        #
        # Call the wrapped method and save the results
        #
        self.curs.execute(operation, parameters, *args, **kwargs)

        #
        # Update the column descriptions for dtuple
        #
        self.update_columns()

        #
        # Return self so we can iterate over the results
        #
        return self

    #
    # .executemany(operation,seq_of_parameters)
    #
    #     Prepare a database operation (query or command) and then
    #     execute it against all parameter sequences or mappings
    #     found in the sequence seq_of_parameters.
    #
    #     Modules are free to implement this method using multiple
    #     calls to the execute() method or by using array operations
    #     to have the database process the sequence as a whole in
    #     one call.
    #
    #     Use of this method for an operation which produces one or
    #     more result sets constitutes undefined behavior, and the
    #     implementation is permitted (but not required) to raise 
    #     an exception when it detects that a result set has been
    #     created by an invocation of the operation.
    #
    #     The same comments as for execute() also apply accordingly
    #     to this method.
    #
    #     Return values are not defined.
    #
    def executemany(self, operation, seq_of_parameters, *args, **kwargs):

        #
        # Call the wrapped method and save the results
        #
        self.curs.executemany(operation, seq_of_parameters, *args, **kwargs)

        #
        # Update the column descriptions for dtuple
        #
        self.update_columns()

        #
        # Return self so we can iterate over the results
        #
        return self

    #
    # .fetchone()
    #
    #     Fetch the next row of a query result set, returning a
    #     single sequence, or None when no more data is
    #     available. [6]
    #
    #     An Error (or subclass) exception is raised if the previous
    #     call to executeXXX() did not produce any result set or no
    #     call was issued yet.
    #
    def fetchone(self, *args, **kwargs):

        row = self.curs.fetchone(*args, **kwargs)

        #
        # Return results using dtuple
        #
        if row:
            return dtuple.DatabaseTuple(self.columns, row)
        else:
            return None

    #
    # .fetchmany([size=cursor.arraysize])
    #
    #     Fetch the next set of rows of a query result, returning a
    #     sequence of sequences (e.g. a list of tuples). An empty
    #     sequence is returned when no more rows are available.
    #
    #     The number of rows to fetch per call is specified by the
    #     parameter.  If it is not given, the cursor's arraysize
    #     determines the number of rows to be fetched. The method
    #     should try to fetch as many rows as indicated by the size
    #     parameter. If this is not possible due to the specified
    #     number of rows not being available, fewer rows may be
    #        returned.
    #
    #     An Error (or subclass) exception is raised if the previous
    #     call to executeXXX() did not produce any result set or no
    #     call was issued yet.
    #
    #     Note there are performance considerations involved with
    #     the size parameter.  For optimal performance, it is
    #     usually best to use the arraysize attribute.  If the size
    #     parameter is used, then it is best for it to retain the
    #     same value from one fetchmany() call to the next.
    #
    def fetchmany(self, size=None, *args, **kwargs):
        size = size or self.arraysize
        return [dtuple.DatabaseTuple(self.columns, row) for row in self.curs.fetchmany(size, *args, **kwargs)]

    #
    # .fetchall()
    #
    #     Fetch all (remaining) rows of a query result, returning
    #     them as a sequence of sequences (e.g. a list of tuples).
    #     Note that the cursor's arraysize attribute can affect the
    #     performance of this operation.
    #
    #     An Error (or subclass) exception is raised if the previous
    #     call to executeXXX() did not produce any result set or no
    #     call was issued yet.
    #
    def fetchall(self, *args, **kwargs):
        return [dtuple.DatabaseTuple(self.columns, row) for row in self.curs.fetchall(*args, **kwargs)]

    #
    # .nextset()
    #
    #     (This method is optional since not all databases support
    #     multiple result sets. [3])
    #
    #     This method will make the cursor skip to the next
    #     available set, discarding any remaining rows from the
    #     current set.
    #
    #     If there are no more sets, the method returns
    #     None. Otherwise, it returns a true value and subsequent
    #     calls to the fetch methods will return rows from the next
    #     result set.
    #
    #     An Error (or subclass) exception is raised if the previous
    #     call to executeXXX() did not produce any result set or no
    #     call was issued yet.
    #
    def nextset(self, *args, **kwargs):
        if hasattr(self.curs, 'nextset'):
            return self.curs.nextset(*args, **kwargs)
        else:
            return None

    #
    # .arraysize
    #
    #     This read/write attribute specifies the number of rows to
    #     fetch at a time with fetchmany(). It defaults to 1 meaning
    #     to fetch a single row at a time.
    #
    #     Implementations must observe this value with respect to
    #     the fetchmany() method, but are free to interact with the
    #     database a single row at a time. It may also be used in
    #     the implementation of executemany().
    #
    arraysize = property(lambda self: self.curs.arraysize)

    #
    # .setinputsizes(sizes)
    #
    #     This can be used before a call to executeXXX() to
    #     predefine memory areas for the operation's parameters.
    #
    #     sizes is specified as a sequence -- one item for each
    #     input parameter.  The item should be a Type Object that
    #     corresponds to the input that will be used, or it should
    #     be an integer specifying the maximum length of a string
    #     parameter.  If the item is None, then no predefined memory
    #     area will be reserved for that column (this is useful to
    #     avoid predefined areas for large inputs).
    #
    #     This method would be used before the executeXXX() method
    #     is invoked.
    #
    #     Implementations are free to have this method do nothing
    #     and users are free to not use it.
    #
    def setinputsizes(self, *args, **kwargs):
        return self.curs.setinputsizes(*args, **kwargs)

    #
    # .setoutputsize(size[,column])
    #
    #     Set a column buffer size for fetches of large columns
    #     (e.g. LONGs, BLOBs, etc.).  The column is specified as an
    #     index into the result sequence.  Not specifying the column
    #     will set the default size for all large columns in the
    #     cursor.
    #
    #     This method would be used before the executeXXX() method
    #     is invoked.
    #
    #     Implementations are free to have this method do nothing
    #     and users are free to not use it.
    #
    def setoutputsize(self, *args, **kwargs):
        return self.curs.setoutputsize(*args, **kwargs)

    #
    # Optional DBAPI Extension
    #
    # Cursor Attribute .rownumber
    #
    #     This read-only attribute should provide the current 0-based
    #     index of the cursor in the result set or None if the index cannot
    #     be determined.
    #
    #     The index can be seen as index of the cursor in a sequence (the
    #     result set). The next fetch operation will fetch the row
    #     indexed by .rownumber in that sequence.
    #
    #     Warning Message: "DB-API extension cursor.rownumber used"
    #
    # NOT CURRENTLY IMPLEMENTED
    #

    #
    # Optional DBAPI Extension
    #
    # Cursor Method .scroll(value[,mode='relative'])
    #
    #     Scroll the cursor in the result set to a new position according
    #     to mode.
    #
    #     If mode is 'relative' (default), value is taken as offset to
    #     the current position in the result set, if set to 'absolute',
    #     value states an absolute target position.
    #
    #     An IndexError should be raised in case a scroll operation would
    #     leave the result set. In this case, the cursor position is left
    #     undefined (ideal would be to not move the cursor at all).
    #
    #     Note: This method should use native scrollable cursors, if
    #     available , or revert to an emulation for forward-only
    #     scrollable cursors. The method may raise NotSupportedErrors to
    #     signal that a specific operation is not supported by the
    #     database (e.g. backward scrolling).
    #
    #     Warning Message: "DB-API extension cursor.scroll() used"
    #
    # NOT CURRENTLY IMPLEMENTED
    #

    #
    # Optional DBAPI Extension
    #
    # Cursor Attribute .messages
    #
    #     This is a Python list object to which the interface appends
    #     tuples (exception class, exception value) for all messages
    #     which the interfaces receives from the underlying database for
    #     this cursor.
    #
    #     The list is cleared by all standard cursor methods calls (prior
    #     to executing the call) except for the .fetchXXX() calls
    #     automatically to avoid excessive memory usage and can also be
    #     cleared by executing "del cursor.messages[:]".
    #
    #     All error and warning messages generated by the database are
    #     placed into this list, so checking the list allows the user to
    #     verify correct operation of the method calls.
    #
    #     The aim of this attribute is to eliminate the need for a
    #     Warning exception which often causes problems (some warnings
    #     really only have informational character).
    #
    #     Warning Message: "DB-API extension cursor.messages used"
    #
    # NOT CURRENTLY IMPLEMENTED
    #

    #
    # Optional DBAPI Extension
    #
    # Cursor Method .next()
    #
    #     Return the next row from the currently executing SQL statement
    #     using the same semantics as .fetchone().  A StopIteration
    #     exception is raised when the result set is exhausted for Python
    #     versions 2.2 and later. Previous versions don't have the
    #     StopIteration exception and so the method should raise an
    #     IndexError instead.
    #
    #     Warning Message: "DB-API extension cursor.next() used"
    #
    def next(self):

        row = self.curs.fetchone()

        if row:
            return dtuple.DatabaseTuple(self.columns, row)
        else:
            raise StopIteration

    #
    # Optional DBAPI Extension
    #
    # Cursor Method .__iter__()
    #
    #     Return self to make cursors compatible to the iteration protocol.
    #
    #     Warning Message: "DB-API extension cursor.__iter__() used"
    #
    def __iter__(self):
        return self

    #
    # Optional DBAPI Extension
    #
    # Cursor Attribute .lastrowid
    #
    #     This read-only attribute provides the rowid of the last
    #     modified row (most databases return a rowid only when a single
    #     INSERT operation is performed). If the operation does not set
    #     a rowid or if the database does not support rowids, this
    #     attribute should be set to None.
    #
    #     The semantics of .lastrowid are undefined in case the last
    #     executed statement modified more than one row, e.g. when
    #     using INSERT with .executemany().
    #
    #     Warning Message: "DB-API extension cursor.lastrowid used"
    #
    # NOT CURRENTLY IMPLEMENTED
    #