:Version: #ident "@(#) $Id: README,v 1.32 2003/07/14 21:35:57 ballie01 Exp $"

----------------------------------------------------------------------------
pyPgSQL - v2.4: Python DB-API 2.0 Compliant Interface Module for PostgreSQL.
----------------------------------------------------------------------------
===============================
0. Copyright notice and License
===============================

    pyPgSQL, version 2.4
    A Python DB-API 2.0 compliant interface for PostgreSQL
    Copyright 2000 by Billy G. Allie.
    All rights reserved.

    Permission to use, copy, modify, and distribute this software and it's
    documentation for any purpose and without fee is hereby granted,
    provided that the above copyright notice appear in all copies and that
    both that copyright notice and this permission notice appear in
    supporting documentation, and that the copyright owner's name not be
    used in advertising or publicity pertaining to distribution of the
    software without specific, written prior permission.

    THE AUTHOR(S) DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
    INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS.  IN
    NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY SPECIAL, INDIRECT OR
    CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
    USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
    OTHER TORTUOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
    PERFORMANCE OF THIS SOFTWARE.

=================
1.  About pyPgSQL
=================

1.1 Introduction
----------------

PostgreSQL is a sophisticated Object-Relational DBMS, supporting almost all SQL
constructs, including sub-selects, transactions, and user-defined types and
functions. It is the most advanced open-source database available anywhere More
information about PostgreSQL can be found at the PostgreSQL home page at
http://www.postgresql.org.

Python is an interpreted, interactive, object-oriented programming language.
It combines remarkable power with very clear syntax.  It has modules, classes,
exceptions, very high level dynamic data types, and dynamic typing.  There are
interfaces to many system calls and libraries, as well as to various windowing
systems (X11, Motif, Tk, Mac, MFC).  New builtin modules are easily written in
C or C++.  Python is also usable as an extension language for applications that
need a programmable interface.  Python is copyrighted but freely usable and
distributable, even for commercial use.  More information about Python can be
found on the Python home page at http://www.python.org.

pyPgSQL is a package of two (2) modules that provide a Python DB-API 2.0
compliant interface to PostgreSQL databases.  The first module, libpq,
exports the PostgreSQL C API to Python.  This module is written in C and
can be compiled into Python or can be dynamically loaded on demand.  The
second module, PgSQL, provides the DB-API 2.0 compliant interface and
support for various PostgreSQL data types, such as INT8, NUMERIC, MONEY,
BOOL, ARRAYS, etc.  This module is written in Python.  This version works
with PostgreSQL 7.0 or later and Python 2.0 or later.

pyPgSQL was originally developed on a UnixWare 7.1.1 system, but is nowadays
also developed on FreeBSD and various Windows and Linux flavours.

1.2 Distribution Files
----------------------

    :README:                    This file.
    :Announce:                  Announcement of this release.
    :ChangeLog:                 changes to this package during it's history.
    :libpqmodule.c:             the C code implementing the libqp module.
    :pgboolean.[ch]:            the C code implementing the PostgreSQL BOOL
                                type object for Python.
    :pgconnection.[ch]:         the C code implementing the PgConnection
                                class.
    :pgint2object.[ch]:         the C code implementing the PostgreSQL INT2
                                type object for Python.
    :pgint8object.[ch]:         the C code implementing the PostgreSQL INT8
                                type object for Python.
    :pglargeobject.[ch]:        the C code implementing the PgLargeObject
                                class.
    :pgnotify.[ch]:             the C code implementing the PgNotify class.
    :pgresult.[ch]:             the C code implementing the PgResult class.
    :pgversion.[ch]:            the C code implementing the PgVersion
                                class.
    :pymemstrdup.c:             the C code implementing a version of strdup()
                                that uses Python's heap for the needed memory.
    :pyPgSQL/__init__.py:       the initialization code for the pyPgSQL
                                package.
    :pyPgSQL/PgSQL.py:          the module that implements the Python DB-API 2.0
                                compliant interface to PostgreSQL
    :pyPgSQL/libpq:             the package for the libpq module.
    :pyPgSQL/libpq/__init__.py: the initialization code for the libpq
                                package.
    :setup.py:                  Distutil setup file for building and installing
                                pyPgSQL
    :port/*:                    String functions imported from the FreeBSD
                                source tree and given a pg prefix.
    :test/PgSQLTestCases.py:    A set of functional test cases built using
                                the Python Unit Testing Framework (PyUnit)
    :test/regression/*:         Test cases to test specific sections of
                                pyPgSQL.
    :examples/*:                Some example programs using libpq and PgSQL

1.3 Installation
----------------

These instructions assume you have Python 2.0 (or later) and at least
PostgreSQL 7.0 (7.2 or later recommended) installed on your system.  If you are
going to use the DB-API 2.0 compliant module, you must also install the
mxDateTime module from http://starship.python.net/~lemburg/mxDateTime.html.

a.  Download pyPgSQL files if you haven't already done so.

b.  Edit the setup.py file to reflect the your environment.  The setup.py file
    contains comments regarding USE_CUSTOM to guide you in customizing this
    file.

c.  Execute ``python setup.py build`` to build the extension module.

d.  Execute ``python setup.py install`` to install the extension module.

(On many platforms, you can skip step b. as the necessary paths are
automatically detected.)

:NOTE:  You may require root access to install the module.
	Consult your local system administrator.

1.4 Testing the PgSQL module.
-----------------------------

To run the tests, enter the following command from the PgSQL source
directory:

    ``python test/PgSQLTestCases.py``

If the test cases run without any failures, then you can be reasonably sure
that the module built correctly.

There are additional test cases in test/regression that you can run. These
require that an empty database *pypgsql* exists locally with *UNICODE*
encoding and with the ability to execute PL/pgsql functions. You can create
such a database with the following commands::

	createdb -E UNICODE pypgsql
	createlang plpgsql pypgsql

1.5 Additional information about ...
------------------------------------

Additional information about the different packages is available at:

    :Python:            http://www.python.org
    :PostgreSQL:        http://www.PostgreSQL.org
    :mxDateTime:        http://starship.python.net/~lemburg/mxDateTime.html

===========================
2.  Programming Information
===========================

2.1 The libpq module
--------------------
	
2.1.1 Importing libpq
---------------------

The module, libpq, is part of the pyPgSQL package.  It is imported using
the following statement:

    >>> from pyPgSQL import libpq


2.1.2 libpq Constants
----------------------

There are a number of constants defined in libpq.  They are intended to be
used as parameters for method calls and to compare against certain results
generated by method calls.  You should refer to the libpq section of the
PostgreSQL programmer's manual for information about them.  These constants
are:

    Connection related constants:

        CONNECTION_OK, CONNECTION_BAD, POLLING_FAILED, POLLING_READING,
        POLLING_WRITING, POLLING_OK, POLLING_ACTIVE

    Query related constants:

        EMPTY_QUERY, COMMAND_OK, TUPLES_OK, COPY_OUT, COPY_IN,
        BAD_RESPONSE, NONFATAL_ERROR, FATAL_ERROR

    Large Object related constants:

        INV_SEEK_SET, INV_SEEK_CUR, INV_SEEK_END, INV_READ, INV_WRITE

    Constants for PostgreSQL type (OID) identifiers:

        Character String Types:

            PG_TEXT, PG_CHAR, PG_VARCHAR, PG_NAME, PG_BPCHAR

        Number Types:

            PG_INT4, PG_INT2, PG_INT8, PG_OID, PG_NUMERIC, PG_FLOAT8,
            PG_FLOAT4, PG_MONEY (aka PG_CASH)

        Temporal Types:

            PG_DATE, PG_TIME, PG_TIMESTAMP, PG_TIMESTAMPTX, PG_INTERVAL,
            PG_ABSTIME, PG_RELTIME, PG_TINTERVAL

        Logical (boolean) Type:

            PG_BOOL

        Geometric Types:

            PG_POINT, PG_LSEG, PG_PATH, PG_BOX, PG_LINE, PG_CIRCLE,
            PG_POLYGON

        Network Types:

            PG_INET, PG_CIDR

        Misc. Types:

            PG_REFCURSOR

The following constants are defined for use by the libpq module and have no
direct relationship to constants in PostgreSQL's C API:

    PgResult related constants:

        :RESULT_DDL:   result was generated by a DDL query.
        :RESULT_DQL:   result was generated by a DQL query.
        :RESULT_DML:   result was generated by a DML query.
        :RESULT_EMPTY: query generated an empty result.
        :RESULT_ERROR: query generated an error.

    PgBoolean constants:

        PgTrue, PgFalse

2.1.3 libpq Methods
-------------------

The following methods are defined by libpq:

    :PQconnectdb:           preferred method to connect to a database.
    :PQconndefaults:        returns a list containing the connection
                            defaults.
    :PQresStatus:           returns a string representation of the result
                            status.
    :PQresType:             returns a string representation of the result
                            type.
    :PQftypeName:           returns a string name for a PostgreSQL type
                            (oid).
    :PgBoolean:             creates a PgBoolean object from a string or
                            number.
    :PgBooleanFromString:   Deprecated, use PgBoolean().
    :PgBooleanFromInteger:  Deprecated, use PgBoolean().
    :PgInt2:                creates a PgInt2 object from a string or
                            number.
    :PgInt8:                creates a PgInt8 object from a string or
                            number.
    :PgLargeObject:         creates a PgLargeObject from a connection and
                            OID.
    :PgVersion:             creates a PgVersion object from a string.
    :PgQuoteString:         Quotes a string, escaping any characters as
                            needed, for use as input to a character/text
                            field.
    :PgQuoteBytea:          Escapes a string, which can contain NUL
                            characters, so that it can used as an input to
                            a bytea field.
    :PgUnQuoteBytea:        Reverses the action of PgQuoteBytea().

2.1.3.1 PQconnectdb
-------------------

*Syntax*:
    c = PQconnectdb(conninfo)

    Where conninfo is a string containing connection information.

*Returns*:
    A PgConnection object.

*Description*:
    Implements the PostgreSQL C API's PQconnectdb function.

*Exceptions*:
    DatabaseError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.3.2 PQconndefaults
----------------------

*Syntax*:
    l = PQconndefaults()

*Returns*:
    A list of default connection options.  A default connection options is
    a list containing [keyword, envvar, compiled, val, label, dispchar,
    dispsize].

*Description*:
    Implements the PostgreSQL C API's PQconndefaults function.

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.3.3 PQresStatus
-------------------

*Syntax*:
    s = PQresStatus(status)

*Returns*:
    A string representation of the result status code, 'status'.

*Description*:
    Implements the PostgreSQL C API's PQresStatus function.

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.3.4 PQresType
-----------------

*Syntax*:
    s = PQresType(type)

*Returns*:
    A string representation of the result type, 'type'.

*Description*:
    The result type is generated by the libpq module (not by the PostgreSQL
    C API library) and describes the result type (DDL, DQL, DML, EMPTY, or
    ERROR).

*Exceptions*:
    InterfaceError

*Returns*:
    A string representation of the result type code, 'type'.

2.1.3.5 PQftypeName
-------------------

*Syntax*:
    s = PQftypeName(type)

*Returns*:
    A string representation of the PostgreSQL type, 'type'.

*Description*:
    This method returns a string representation of the PostgreSQL type,
    'type'.  This string is useful for displaying the type code.  This
    method has no corresponding PostgreSQL C API function.

2.1.3.6 PgBoolean
-----------------

*Syntax*:
    b = PgBoolean(object)

*Description*:
    This method returns a PgBoolean object initialized from the
    value of object.  It recognizes the following string values:

	For true.: '1', 'T', 'TRUE', 'Y', 'YES', 'ON'
	For false: '0', 'F', 'FALSE', 'N', 'NO', 'OFF'

    For numeric object, zero is false, non-zero is true.

*Returns*:
    PgTrue or PgFalse based on the value of 'object'

2.1.3.7 PgInt2
--------------

*Syntax*:
    n = PgInt2(object)

*Description*:
    This method returns a PgInt2 object initialized from the value of the
    string or numeric 'object'.  The PgInt2 type uses a 2-byte integer to
    store it's value.

*Returns*:
    A PgInt2 object initialized with the value of 'object'.

2.1.3.8 PgInt8
--------------

*Syntax*:
    n = PgInt8(object)

*Description*:
    This method returns a PgInt8 object initialized from the value of the
    string or numeric 'object'.  The PgInt8 type uses a 8-byte integer to
    store it's value.

*Returns*:
    A PgInt8 object initialized with the value of 'object'.

2.1.3.9 PgLargeObject
---------------------

*Syntax*:
    o = PgLargeObject(PgConnection, OID)

*Description*:
    This function will create a PgLargeObject object given a PgConnection
    object and a PostgreSQL large object identifier (OID).

*Returns*:
    A closed PgLargeObject object.

*Note*:
    A PgLargeObject can not be opened outside the context of a transaction.
    Because of this, large objects created with this method (and by
    inference, un-pickled large objects) will begin a transaction (if
    needed) in it's associated PgConnection object when the the large
    object is opened.  When the large object is closed, the transaction
    will be committed.  If a rollback is desired, pass close() an argument
    of 1.

2.1.3.10 PgQuoteString
----------------------

*Syntax*:
    s = PgQuoteString(string, forArray)

*Description*:
    This function returns a copy of the input string with the
    following characters escaped::

	1.  The backslash character (as '\\')
	2.  The single quote (as "\'")
	3.  The <CR> character (as '\r')
	4.  The <NL> character (as '\n')
	5.  The <BS> character (as '\b')
	6.  The <FF> character (as '\f')
	7.  The <TAB> character (as '\t')
	8.  All other control characters as '\OOO' where OOO is
	    the octal representation of the character's ordinal
	    number.
	The string is also quoted with single quotes.

	If forArray is one (1), the escaping is changed  as follows:
	    1.  The backslash character (as '\\\\')
	    (2 through 7 remain the same)
	    8.  All other control characters as '\\\\000'
	    9.  The double quote (as '\"')
	The string is also quoted with double quotes, instead of single
	quotes.

*Returns*:
    A quoted, escaped copy of the input string.

2.1.3.11 PgQuoteBytea
---------------------

*Syntax*:
    s = PgQuoteBytea(string)

*Description*:
    This function returns a copy of the input string with characters
    escaped as follows::

	1.  <NUL> characters: '\\000' (Note: with 2 backslashes)
	2.  Non-printable characters: '\OOO' (Note OOO is the octal
	    representation of the characters ordinal number)
	3.  Backslashes: '\\\\' (Note: with 4 backslashes)
	4.  Single quote: "\'"
	The string is also quoted with single quotes.


	If forArray is one (1), the escaping is changed  as follows:
	    1.  <NUL> characters: '\\\\000' (Note: with 4 backslashes)
	    2.  Non-printable characters: '\\\\OOO'
	    3.  Backslashes: '\\\\\\\\' (Note: with 8 backslashes)
	    4.  Single quote: "\'"
	    5.  The double quote (as '\\"')
	The string is also quoted with double quotes, instead of single
	quotes.

*Returns*:
    A quoted, escaped copy of the input string.

2.1.3.12 PgUnQuoteBytea
-----------------------

*Syntax*:
    s = PgUnQuoteBytea(string)

*Description*:
    This function un-escapes a string retrieved from a bytea field.

*Returns*:
    A copy of the input string with any escaped character returned
    to their original value.

2.1.4 libpq Classes
-------------------

This module defines the following five (5) classes:

    :PgConnection:  the connection class.  It handles the connection and all
                    requests to the database.
    :PgResult:      handles the query results.
    :PgLargeObject: handles the access to PostgreSQL large objects.
    :PgNotify:      the notify class.  It contains information about a
                    notification event sent from a PostgreSQL backend process.
    :PgVersion:     the version class.  It contains information about the
                    version of the PostgreSQL backend that a connection
                    object is connected to.

The module makes error information available via the following exception
objects, in addition to the standard Python exceptions:

    Warning, Error, InterfaceError, DatabaseError, OperationalError,
    IntegrityError, InternalError, ProgrammingError, NotSupportedError

Additional information about these exceptions can be found in the Python
DB-API 2.0 documentation.

2.1.4.1 The PgConnection Object
-------------------------------

The PgConnection Object defines a connection to the PostgreSQL database.
It has the following public, read-only attributes:

    :host:         The server host name of the connection.  It returns the
                   output of the PQhost PostgreSQL C API function.
    :post:         The port used in the connection.  It returns the output of
                   the PQport function.
    :db:           The database name of the connection.  It returns the output
                   of the PQdb function.
    :options:      The backend options used in the connection.  It returns the
                   output of the PQoptions function.
    :tty:          The debug tty of the connection.  It returns the output of
                   the PQtty function.
    :user:         The user name of the connection.  It returns the output of
                   the PQuser function.
    :status:       The status of the connection.  It returns the output of the
                   PQstatus function.
    :errorMessage: The error message most recently generated by an operation
                   on the connection.  It returns the output of the
                   PQerrorMeesage function.
    :backendPID:   The process ID of the backend handling this connection.  It
                   returns the output of the backendPID function.
    :isBusy:       Indicates if PQgetResult would block.  Used with
                   asynchronous query processing.  It returns the output of
                   the PQisBusy function (PostgreSQL 7.0 or later).
    :socket:       The file descriptor for the backend connection socket.
                   Used with asynchronous query processing.  It returns the
                   output of the PQsocket function.
    :notices:      A list of notices received by the PostgreSQL C API.  The
                   notices are placed in the list so that the list.pop()
                   method will retrieve the oldest notice on the list.

                   :NOTE:  While this attribute is read-only, you can still
			   manipulate the list using any of the list's methods
			   (pop, append, insert, etc.).  You just can't assign
			   a new value to the attribute.

    :version:      version information about the backend that this connection
                   object is connected to.

The PgConnection Object has the following methods:

    :connectPoll:    Poll the libpq C API for the connection status.
    :query:          Execute a query and wait for the results.
    :sendQuery:      Send a query to the backend without blocking.
    :getResult:      Retrieve the results from the sendQuery method.
    :setnonblocking: Make the connection non-blocking (or blocking).
    :consumeInput:   If input is available from the backend, consume it.
    :flush:          Attempt to flush any data queued on the backend.
    :requestCancel:  Send a cancel query request to the backend.
    :finish:         Close the connection and free memory used by the PQconn
                     object.
    :reset:          Reset the communication port with the backend.
    :notifies:       Returns the next notification object (PgNotify) from a list
                     of unhandled notification objects.
    :getline:        Read a (newline-terminated) line of characters from the
                     backend.
    :getlineAsync:   Read a line of characters in a non-blocking manner.
    :putline:        Send a null-terminated string to the backend.
    :endcopy:        Sync with the backend (after a Copy-In/Copy-Out operation).
    :lo_creat:       Create a new, empty PgLargeObject.
    :lo_import:      Import a file as a PostgreSQL large object, returning a
                     PgLargeObject.
    :lo_export:      export a PostgreSQL large object to a file.
    :lo_unlink:      Removes a PostgreSQL large object from the database.
    :trace:          Enable tracing of frontend/backend communications.
    :untrace:        Disable tracing start by the trace method.

2.1.4.1.1 connectPoll (PostgreSQL 7.x and above)
------------------------------------------------

*Syntax*:
    i = c.connectPoll()

*Returns*:
    An integer representing a Postgres Polling Status code.

*Description*:
    This method is used to determine the status of a connection started
    with PQconnectStart().  This method implements the PQconnectPoll()
    function and is used for asynchronous query processing.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.2 query
---------------

*Syntax*:
    r = c.query(string)

*Returns*:
    A PgResult object.

*Description*:
    This method sends the SQL query, 'string', to the backend and
    waits for the result.  It implement the PostgreSQL C API's
    PQexec function.

*Exceptions*:
    InterfaceError, ProgrammingError, OperationalError,
    InternalError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.3 sendQuery
-------------------

*Syntax*:
    c.sendQuery(string)

*Description*:
    This method send the SQL query, 'string', to the backend without
    waiting for the result.  It implements the PQsendQuery function and is
    used for asynchronous query processing.

*Exceptions*:
    InternalError, InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.4 getResult
-------------------

*Syntax*:
    r = c.getResult()

*Returns*:
    A PgResult object.

*Description*:
    Wait for and retrieve the results from a previous sendQuery call.  It
    implements the PQgetResult function and is used for asynchronous query
    processing.

*Exceptions*:
    InterfaceError, ProgrammingError, OperationalError,
    InternalError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.5 setnonblocking (PostgreSQL 7.x and above)
---------------------------------------------------

*Syntax*:
    c.setnonblocking(mode)

*Description*:
    Set the connection to non-blocking if 'mode' is non-zero, otherwise set
    it to blocking.  This method implements the PQsetnonblocking()
    function.

*Exceptions*:
    InterfaceError, InternalError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.6 consumeInput
----------------------

*Syntax*:
    c.consumeInput()

*Description*:
    If input is available from the backend, consume it.  This method
    implements the PQconsumeInput function and is used with asynchronous
    query processing.

*Exceptions*:
    InterfaceError, InternalError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.7 flush (PostgreSQL 7.x and above)
------------------------------------------

*Syntax*:
    c.flush()

*Description*:
    If input is available from the backend, consume it.  This method
    implements the PQflush function and is used with asynchronous query
    processing.

*Exceptions*:
    InterfaceError, InternalError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.8 requestCancel
-----------------------

*Syntax*:
    c.requestCancel()

*Description*:
    Send a cancel request to the backend.  Note that the successful
    dispatching of the request does not mean the request will be canceled.
    This method implements the PQrequestCancel function and is used with
    asynchronous query processing.

*Exceptions*:
    InterfaceError, InternalError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.9 finish
----------------

*Syntax*:
    c.finish()

*Description*:
    Close the connection to the database and invalidates the PgConnection
    object.  Any attempt to use the PgConnection object after finish is
    called will raise an InterfaceError.  Used by the PQconn object.  The
    database connection is automatically closed when the PgConnection
    object is deleted, so calling finish explicitly is never needed. This
    method implements and extends the PQfinish function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.10 reset
----------------

*Syntax*:
    c.reset()

*Description*:
    Close the connection to the backend and attempt to open a new
    connection using the previously used parameters.  This method
    implements the PQreset function.

*Exceptions*:
    InterfaceError, DatabaseError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.11 notifies
-------------------

*Syntax*:
    n = c.notifies()

*Returns*:
    A PgNotify object containing data for the next notification message, or
    None if there are no unhandled notifications.

*Description*:
    Retrieves the next notification from a list of unhandled notification
    messages received from the backend.  Once a notification object is
    returned, it is considered handled and will be removed from the list of
    notifications.  This method implements the PQnotifies function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.12 getline
------------------

*Syntax*:
    s = c.getline()

*Returns*:
    A newline-terminated string read from the backend.

*Description*:
    The getline method reads a newline-terminated string (transmitted by
    the backend server) into a (dynamically sized) buffer.  This method
    implements the PQgetline function and is used with the PostgreSQL COPY
    command.

*Exceptions*:
    InterfaceError, TypeError, MemoryError, InternalError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.13 getlineAsync
-----------------------

*Syntax*:
    s = c.getlineAsync()

*Returns*:
    A newline-terminated string read from the backend in a
    non-blocking manner.

*Description*:
    The getlineAsync method reads a newline-terminated string (transmitted
    by the backend server) into a (dynamically sized) buffer.  This method
    implements the PQgetline function and is used with the PostgreSQL COPY
    command.

*Exceptions*:
    InterfaceError, TypeError, MemoryError, InternalError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.14 putline
------------------

*Syntax*:
    c.putline(s)

*Returns*:
    Sends a string to the backend.

*Description*:
    The putline method sends a (null-terminated) string to the backend.
    This method implements the PQputline function and is used with the
    PostgreSQL COPY command.

*Exceptions*:
    InterfaceError, TypeError, InternalError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.15 endcopy
------------------

*Syntax*:
    c.endcopy()

*Returns*:
    Syncs with the backend.

*Description*:
    This function waits until the backend has finished the copy. It should
    either be issued when the last string has been sent to the backend
    using putline or when the last string has been received from the
    backend using getline. It must be issued or the backend may get "out of
    sync" with the frontend.  This method implements the PQputline function
    and is used with the PostgreSQL COPY command.

*Exceptions*:
    InterfaceError, TypeError, InternalError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.16 lo_creat
-------------------

*Syntax*:
    lo = c.lo_creat(mode)

*Returns*:
    A PgLargeObject.

*Description*:
    Create a PostgreSQL large object with the given mode.  This method
    implements the lo_creat function.

*Exceptions*:
    InterfaceError, OperationalError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.17 lo_import
--------------------

*Syntax*:
    lo = c.lo_import(filename)

*Returns*:
    A PgLargeObject

*Description*:
    Imports a file named 'filename' into a PostgreSQL large object.  This
    method implements the lo_import function.

*Exceptions*:
    InterfaceError, OperationalError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.18 lo_export
--------------------

*Syntax*:
    c.lo_export(oid, filename)

*Returns*:
    A PgLargeObject

*Description*:
    Exports a PostgreSQL large object, represented by oid, to a file named
    'filename'.  This method implements the lo_import function.

*Exceptions*:
    InterfaceError, OperationalError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.19 lo_unlink
--------------------

*Syntax*:
    c.lo_unlink(oid)

*Description*:
    Removes the PostgreSQL large object identified by 'oid' from
    the database.  This method implements the lo_unlink function.

*Exceptions*:
    InterfaceError, IOError, TypeError

2.1.4.1.20 trace
----------------

*Syntax*:
    c.trace(fileObject)

*Description*:
    Enables tracing of the frontend/backend communications to a
    Python File Object, fileObject.  This method implements the
    PQtrace function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.1.21 untrace
------------------

*Syntax*:
    c.untrace()

*Description*:
    Disables tracing enabled by the trace method.  This method
    implements the lo_import function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.2 The PgResult Object
---------------------------

The PgResult object defines the result of a query.  It has the following
public, read-only attributes:

    :resultType:        the type of the result: DDL, DQL, DML, EMPTY, ERROR.
    :resultStatus:      The result status of the query.  It returns the
                        output of the PQresultStatus PostgreSQL C API
                        function.
    :ntuples:           The number of tuples (instances) in the query result.
                        It returns the output of the PQntuples function call.
    :nfields:           The number of fields (attributes) in each tuple of
                        the query result.  It returns the output of the
                        PQnfields function.
    :binaryTuples:      Contains 1 if the PgResult object contains binary
                        tuple data, 0 if it contains ASCII data. It returns
                        the output of the PQbinaryTuples function call.

                        :NOTE: Binary portals are not supported at this time.

    :cmdStatus:         The command status string from the SQL command that
                        generated the PGresult.  It returns the output to the
                        PQcmdStatus function.
    :cmdTuples:         The number of rows affected by the SQL command.  It
                        returns the output of the PQcmdTuples function.
    :oidValue:          (7.x and above) The object id of the tuple
                        inserted, if the SQL command was an INSERT.
                        Otherwise, contains None.  It returns the output of
                        the PQoidValue function.

The PgResult Object has the following methods:

    :fname:     Returns the field (attribute) name associated with the given
                field index.
    :fnumber:   Returns the field (attribute) index associated with the given
                field name.
    :ftype:     Returns the type of a field.
    :fsize:     Returns the size in bytes of the field.
    :fmod:      Returns the type-specific modification data of a field.
    :getvalue:  Returns a single field (attribute) value of one tuple of a
                PgResult.
    :getlength: Returns the length of a field (attribute) in bytes.
    :getisnull: Tests a field for a NULL entry.
    :clear:     Frees the memory used by result.

2.1.4.2.1 fname
---------------

*Syntax*:
    s = r.fname(fidx)

*Returns*:
    The field (attribute) name associate with the given field
    index.

*Description*:
    Returns the field (attribute) name associated with the given
    field index. Field indices start at 0.  It implements the
    PQfname PostgreSQL C API function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.2.2 fnumber
-----------------

*Syntax*:
    i = r.fnumber(name)

*Returns*:
    The field (attribute) index associated with the given field
    name.

*Description*:
    Returns the field (attribute) index associated with the given
    field name, 'name'.  A -1 is returned if the name does not
    match any field.  It implements the PQfnumber function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.2.3 ftype
---------------

*Syntax*:
    i = r.ftype(fidx)

*Returns*:
    Returns the field type associated with the given field index.

*Description*:
    The field type associated with the given field index.  The integer
    returned is an internal coding of the type.  Field indices start at 0.
    It implements the PQftype function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.2.4 fsize
---------------

*Syntax*:
    i = r.fsize(fidx)

*Returns*:
    The size in bytes of the field associated with the given field
    index.

*Description*:
    Returns the size in bytes of the field associated with the
    given field index. Field indices start at 0.  fsize returns
    type).  -1 is returned if the field is variable size.  It
    implements the PQfsize function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.2.5 fmod
--------------

*Syntax*:
    i = r.fmod(fidx)

*Returns*:
    The type-specific modification data of the field associated
    with the given field index

*Description*:
    Returns the type-specific modification data of the field associated
    with the given field index.  Field indices start at 0.  It implements
    the PQfmod function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.2.6 getvalue
------------------

*Syntax*:
    o = r.getvalue(tidx, fidx)

*Returns*:
    A single field (attribute) value of one tuple of a PGresult.

*Description*:
    Returns a single field (attribute) value of one tuple of a
    PgResult.  Tuple and field indices start at 0.  If the field
    is NULL, the None is returned.  The type of object returned
    depends on the PostgreSQL data type of the field:

                    ====================== =====================
                    PostgreSQL Type        Returned Python Object
                    ====================== =====================
                    PG_BOOL                PgBoolean
                    PG_OID                 Integer or PgLargeObject(1)
                    PG_INT2                PgInt2
                    PG_INT4                Integer
                    PG_INT8                PgInt8(2) or Long
                    PG_MONEY               Float
                    PG_FLOAT4              Float
                    PG_FLOAT8              Float
                    PG_BYTEA               String(3)
                    All Other Types        String
                    ====================== =====================

                    (1) getvalue() will determine if the OID represents a
                        PostgreSQL Large Object and returns the appropriate
                        object.
                    (2) PgInt8 type is only available on system that have
                        long long (64 bit integer) support.
                    (3) Any escaped characters in the string will be returned
                        to their original value in the returned string.

                getvalue implements and extends the PQgetvalue function.

*Exceptions*:
    InterfaceError, TypeError

2.1.4.2.7 getlength
-------------------

*Syntax*:
    i = r.getlength(tidx, fidx)

*Returns*:
    The length of a field (attribute) in bytes.

*Description*:
    Returns the length of a field (attribute) in bytes.  Tuple and
    field indices start at 0.  This is the actual data length for
    the particular data value, that is the size of the object
    pointed to by getvalue. Note that for ASCII-represented values,
    this size has little to do with the binary size reported by
    fsize.  It implements the PQgetlength function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.2.8 getisnull
-------------------

*Syntax*:
    i = r.getisnull(tidx, fidx)

*Returns*:
    1 if the field contains a NULL, 0 if it contains a non-null
                value.

*Description*:
    Tests a field for a NULL entry. Tuple and field indices start
    at 0.  This function returns 1 if the field contains a NULL, 0
    if it contains a non-null value.  (Note that getvalue will return None
    for a NULL field.)  It implements the PQgetisnull function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.2.9 clear
---------------

*Syntax*:
    r.clear()

*Description*:
    Frees the storage associated with a PgResult and invalidates
    the PgResult object.  Any attempt to access the PgResult will
    generate an InterfaceError exception.  The PgResult is automatically
    cleared when the PgResult if deleted, so calling clear explicitly is
    never needed.  It implements and extends the PQclear function.

*Exceptions*:
    InterfaceError, TypeError

*Note*:
    See the PostgreSQL C API documentation for details.

2.1.4.3 The PgLargeObject object
--------------------------------

The PgLargeObject class provides methods for accessing the PostgreSQL Large
Object (LO) system.  It allows access to the LO using Python's File Object
semantics. The PgLargeObject class defines the following public, read-only
attributes:

    :mode:   The mode used to open the LO
    :name:   A string, in the form of "<...>", indicating the source of the LO.
    :closed: Flag: 1 = the LO is closed.

and the following public, read-write attribute:

    :softspace: Boolean that indicates whether a space character needs to be
                printed before another value when using the 'print' statement.

The following methods are provided:

    :close:      Close the LO.  A closed LO can not be read or written anymore.
    :flush:      Flush the internal buffer.
    :open:       Open the LO.  A LO can be opened for reading, writing, or both.
    :isatty:     Always returns 0.  A LO is never attached to a TTY like device.
    :fileno:     Returns the integer 'file descriptor' used by the underlining
                 implementation to request I/O operations.
    :read:       Read bytes from the LO.
    :readline:   Read one entire line from the LO.
    :readlines:  Read entire lines from the LO until EOF.
    :seek:       Set the LO's current position, like stdio's fseek().
    :tell:       Returns the LO's current position, like stdio's ftell().
    :write:      Write bytes to the LO.
    :writelines: Write a list of strings to the LO.
    :export:     Export a LO to a file.

Since the PgLargeObject follows Python's File Object semantics, refer to the
documentation for File Objects for details on using PgLargeObject.  There are
a few differences, which will be detailed here.

2.1.4.3.1 open
--------------

*Syntax*:
    lo.open(mode)

*Description*:
    Opens a PostgreSQL Large Object for reading, writing, or both.
    The 'mode' parameter can be either an integer consisting of a
    combination of the INV_READ and INV_WRITE mode bits, or a
    string containing 'r' for reading, or 'w' for writing.  The LO
    can be open for updating by using 'r+' or 'w+'.  A 'b' can be
    included in the mode string to indicate opening the LO for binary data,
    but is not really needed since PostgreSQL does not differentiate
    between binary and non-binary data.

    :NOTE:  'w+' will NOT truncate the large object.

*Note*:
    Open is a built-in function of Python, not a method of the File
    Object.  If there is not transaction started on the associated
    PgConnection object when open is called, one is started.  This
    will only occur for un-pickled large objects and large objects
    created with the PgLargeObject method of libpq (and PgSQL).

2.1.4.3.2 close
---------------

*Syntax*:
    lo.close()

*Description*:
    This method will close an open large object.

*Note*:
    If the large object was the result of un-pickling a large
    object or it was created with the PgLargeObject method of
    libpq (or PgSQL), close() will commit the transaction started
    by open().  If a rollback is desired, then pass close a single
    argument of the integer 1.  This argument is only valid if the
    large object was the result of un-pickling a large object or
    created with the PgLargeObject method.

2.1.4.3.3 export
----------------

*Syntax*:
    i = lo.export(filename)

*Returns*:
    1 if successful, 0 if an OS error occurred, < 0 if a database
    error occurred.

*Description*:
    This method will export the PostgreSQL large object to the
    specified UNIX filename.

*Note*:
    The file is stored on the database server, not the client machine (if
    different from the server).

2.1.4.4 The PgNotify Object
---------------------------

The PgNotify object encapsulates the data returned by the notifies method of
the PgConnection class.  It provides the following read-only attributes:

    :relname:  The name of the relation containing data.
    :be_pid:   The process ID of the PostgreSQL backend sending the
               notification.

2.1.4.5 The PgVersion Object
----------------------------

The PgVersion object encapsulates information about the version of PostgreSQL
that a connection object is connected to.  It provides the following read-only
attribute:

    :major:     The major version number.
    :minor:     The minor version number.
    :level:     The patch level.
    :post70:    A flag that is true if the version is >= 7.1.0.

You can obtain the result of the 'SELECT version()' used to initialize this
object using the str() or repr() function.

For example, for version 6.5.3, the contents of the PgVersion object would be:

    ::

        connection.version        == "PostgreSQL 6.5.3 on <system dependent info>"
        connection.version.major  == 6
        connection.version.minor  == 5
        connection.version.level  == 3
        connection.version.post70 == 0

For example, for version 7.1.1, the contents of PgVer would be:

    ::

	connection.version        == "PostgreSQL 7.1.1 on <system dependent info>"
	connection.version.major  == 7
	connection.version.minor  == 1
	connection.version.level  == 1
	connection.version.post70 == 1

Also, you can use the PgVersion object to compare against a number or string
form of the version.  The form used for numeric comparison is "Mmmll", where
"M" is the major number, "mm" is the minor number, and "ll" is the patch level.
An example:

    Assume that the PostgreSQL version is 7.0.2, then:

        ::

	    connection.version == 70002 will be true.
	    connection.version < 70001L will be false.
	    connection.version > 70001.0 will be true.

You can also compare against a string as follows:

    Assume that the PostgreSQL version is 7.1.2, then:

        ::

	    connection.version == "7.0.2" will be false.
	    connection.version < "7.0.1" will be false.
	    connection.version > "7.1" will be true.

:NOTE:  Both the libpq and PgSQL connection objects have the version attribute.

:NOTE:  Comparisons against strings (i.e. "7.0.1") does not work in
	Python 2.0.

2.2 The PgSQL module
--------------------

The PgSQL module provide a Python DB-API 2.0 compliant module on top of the
libpq module.  As the DB-API 2.0 interface is documented elsewhere
(http://www.python.org/topics/database/DatabaseAPI-2.0.html), I will only
describe the differences in the PgSQL here.

2.2.1 Importing PgSQL
---------------------

The module, PgSQL, is part of the pyPgSQL package.  It is imported using
the following statement:

    >>> from pyPgSQL import PgSQL

2.2.2 Differences at the Module Level
-------------------------------------

1.  The Binary constructor is a method of the Connection object, not the module.
    For PostgreSQL, a Large Object can only be created in conjunction with a
    Connection, it has no meaning outside of the context of a Connection.

2.  The following types are defined to support certain PostgreSQL data types:

    :PgInt2:    Supports the PG_INT2 data type.

    :PgInt8:    Supports the PG_INT8 data type.

    :PgBoolean: Supports the PG_BOOL data type.

3.  The following classes are defined to support certain PostgreSQL data types:

    :PgNumeric: Supports the PG_NUMERIC data type.  It uses a Python Long as
                the base type and provides the following arithmetic operations:
                addition, subtraction, multiplication, and division.

    :PgMoney:   Supports the PG_CASH data type.  It uses a Python Float as the
                base type with range checking to prevent it from exceeding the
                range of the PG_CASH data type.  Any operation that applies to
                a Python Float can be used with a PgMoney object.

    :PgBytea:   This class supports the PG_BYTEA data type.  It is a wrapper
                around a Python String that provides for proper escaping of
                the string when used in a query.

    :PgOther:   This class supports all the other PostgreSQL data types that
                do not map directly into a Python object or one of the support
                classes listed above (such as PG_BOX, PG_POINT, etc.).  As time
                goes on, more PostgreSQL data types will have support classes
                defined for them, reducing the number of PostgreSQL data types
                that fall within this class.

    :PgArray:   This class provide support for PostgreSQL arrays.  It is a
                wrapper around a Python list that supports all the methods of
                a list plus adds a __quote__ method for quoting arrays.

4.  The following class is defined:

    :PgVersion: Contains the version number of PostgreSQL database engine that
                we are connected to.  This information is used to change the
                behavior of PgSQL based on the version of the PostgreSQL
                engine.  See the section 2.6 for more details on the
                PgVersion object.

5.  The following constructors are defined by the PgSQL module.

    :PgBoolean:         Construct a PgBoolean from a Python numeric or string.
    :PgInt2:            Construct a PgInt2 from a Python numeric or string.
    :PgInt8:            Construct a PgInt8 from a Python numeric or string.
    :PgLargeObject:     Construct a PgLargeObject from a PgConnection object and
                        a OID identifying a PostgreSQL large object.

    These constructors are documented in the libpq section of this document.

6.  The following attribute is defined in the PgSQL module:

        :fetchReturnsList: controls the type of result returns by the fetchXXX
                           methods.

    Setting this attribute to 1 will cause the fetchXXX methods to return a
    list instead of a PgResultSet.  This will provide better performance by
    sacrificing the convenient access methods provide by a PgResultSet.

    The default value for fetchReturnsList is 0.

2.2.3 Differences in the Connection Object
------------------------------------------

1.  The Connection object has an additional read-only attribute called notices.
    This attribute is a list of notices returned by the pq library.

    :NOTE:  Under normal usage, certain (but not all) notices received from
	    the libpq C-API library are converted into Warning exceptions.

2.  The Connection object has an additional read-only attribute called version.
    This attribute contains a PgVersion object encapsulating the version
    information of the PostgreSQL backend that the Connection object is
    connected to.

3.  The Binary constructor method is a Connection method, not a PgSQL module
    function.

4.  A unlink method is available in the Connection object to remove a Large
    Object from the database.

5.  A PgSQL specific Connection attribute, called TransactionLevel, specifies
    the isolation level to use within a transaction.  It can be set to "",
    "READ COMMITED", or "SERIALIZABLE".  PgSQL will issue the appropriate "SET
    TRANSACTION LEVEL" statement whenever a new transaction is started for
    the connection.

    :NOTE:  The value of this attribute can not be changed if there are any
	    active cursors for the connection.

2.2.3.1 unlink
--------------

*Syntax*:
    c.unlink(PgLargeObject)

*Description*:
    Removes the PostgreSQL large object identified from the
    database.

*Exceptions*:
    InterfaceError, IOError, TypeError

2.2.4 Differences in the Cursor Object
--------------------------------------

1.  The description attribute is a sequence of 8-item sequences.  The first
    seven items are the same as described in the DB-API 2.0 documentation.
    The 8th item is the 'isArray' flag.  If this is 1, then the associated
    result column is a PostgreSQL array.

2.  The callproc method will always return None.  PostgreSQL does not have
    stored procedures in the same sense as other databases such as Oracle.
    There are no 'Input', 'Output', or 'Input/Output' parameters.  In PgSQL,
    this method is used to call PostgreSQL functions, which only return a
    result set (or nothing).

    :NOTE:  Beginning with PostgreSQL 7.2, it is possible to return a
	    reference to a cursor from PL/pgSQL.  PgSQL will create a new
	    Cursor object for the referenced cursor that is returned.

3.  When using the execute method, you should only use '%s' [or '%(name)s']
    (without the quote marks) to specify locations where the parameters are to
    be substituted, even for integers, floats and other non-string variables.
    The execute method will convert all the parameters to a string, applying any
    quoting that may be necessary before sending the query to the back-end.

4.  The fetchone method will return a PgResultSet object instead of a sequence.
    A PgResultSet emulates a Python List object (for DB-API 2.0 compliance),
    but also acts as a dictionary and allows the column data to be retrieved by
    using the column name as an attribute of the PgResultSet object. The column
    names are case-insensitive.

    :NOTE:  This feature is controlled by the fetchReturnsList attribute of
	    the PgSQL module.

5.  The fetchmany and fetchall methods return a sequence of PgResultSet objects
    instead of a sequence of sequences.

    :NOTE:  This feature is controlled by the fetchReturnsList attribute of
	    the PgSQL module.

6.  A PostgreSQL specific attribute, named oidValue, was added to the cursor
    object.  This attribute returns the value of the oidValue attribute of the
    PgResult object associated with the cursor object and provides a convenient
    way to get the object ID of a newly inserted record.

2.2.5 Unicode support
---------------------

pyPgSQL has a few extensions that make it possible to insert Unicode strings
into PostgreSQL and fetch unicode strings instead of byte strings from the
database.

The module-level connect() function has two Unicode-related parameters:

- client_encoding
- unicode_results

*client_encoding* accepts the same parameters as the encode method
of Unicode strings. If you also want to set a policy for encoding
errors, set client_encoding to a tuple, like ("koi8-r", "replace")

Note that you still must make sure that the PostgreSQL client is
using the same encoding as set with the client_encoding parameter.
This is typically done by issuing a "SET CLIENT_ENCODING TO ..."
SQL statement immediately after creating the connection.

If you also want to fetch Unicode strings from the database, set
*unicode_results* to 1.

For example, assuming a database created with *createdb mydb -E UNICODE* and a
table *TEST(V VARCHAR(50))*:

    >>> from pyPgSQL import PgSQL
    >>> cx = PgSQL.connect(database="mydb", client_encoding="utf-8", unicode_results=1)
    >>> cu = cx.cursor()
    >>> cu.execute("set client_encoding to unicode")
    >>> cu.execute("insert into test(v) values (%s)", (u'\x99sterreich',))
    >>> cu.execute("select v from test")
    >>> cu.fetchone()
    [u'\x99sterreich']
    >>>

==================================
3.0 General Notes and Observations
==================================

The PostgreSQL database system has no auto-commit setting.  It is always in
auto-commit mode unless a transaction is started.  To achieve the DB-API 2.0
mandated behaviour, when connection.autocommit is 0, a transaction is
started when the first cursor is created for a connection.  After a commit
or rollback, a new transaction is created on the next call to execute().

----------------------------------------------------------------------------

PostgreSQL arrays are no longer (directly) represented by Python lists.
This means that lists and tuples are not longer treated specially by
Cursor.execute().  This resolves a problem of using the IN SQL syntax with
Cursor.execute().  For example, the following statement will now work:

    >>> Cursor.execute('select * from table where column1 in %s', ((1, 3, 4),))

It will generate the following SQL statement:

    select * from table where column1 in (1, 3, 4)

It also means that to insert an PostgreSQL array, you must pass a PgArray
instance to Cursor.execute().  For example, if you have a list that you want
to insert into a table as a PostgreSQL array, you would use:

    >>> cursor.execute('insert in sometable values (%s)', PgArray(yourlist))

You can also build a PostgreSQL array by creating an empty PgArray instance
and populating it using the various list methods (.append(), .insert(), etc.).

----------------------------------------------------------------------------

When working with PostgreSQL large object, you MUST be in a transaction.
The code will try to ensure that a transaction is active while working with
large object (i.e. lo_open will start a transaction if necessary.)

----------------------------------------------------------------------------

There is a change to the Connection.binary() function that *could* cause
existing code to break.  Connection.binary() no longer commits the trans-
action used to create the large object.  The application developer is now
responsible for commiting (or rolling back) the transaction.

----------------------------------------------------------------------------

Beginning with PostgreSQL 7.2, you can now create a cursor in PL/pgSQL and 
return a reference to that cursor.  PgSQL will transform the reference to
the created cursor into a Cursor object that can be used to fetch the
results of the cursor.  For example (assuming that mmYearInfo returns a
reference cursor):

    >>> from pyPgSQL import PgSQL
    >>> cx = PgSQL.connect(database='esi')
    >>> cu = cx.cursor()
    >>> cu.callproc('mmYearInfo')
    >>> rs = cu.fetchone()
    >>> rs
    [<pyPgSQL.PgSQL.Cursor instance at 0x818495c>]
    >>> c = rs[0]
    >>> for i in c.description:
    ...     print i
    ... 
    ['model_year', varchar, 4, 8, None, None, None, 0]
    ['mktg_div_name', varchar, 50, 54, None, None, None, 0]
    ['model_desc', varchar, 50, 54, None, None, None, 0]
    ['book_types', varchar, 50, 54, None, None, None, 0]
    ['vehicle_syskey', integer, 4, 4, None, None, None, 0]
    >>> r = c.fetchone()
    >>> r
    ['2003', 'Buick', 'Century', '1;8;9', 2211]
    >>>