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@ -63,8 +63,7 @@ PyGreSQL 2.0 was developed and tested on a NetBSD 1.3_BETA system. It is |
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based on the PyGres95 code written by Pascal Andre, andre@chimay.via.ecp.fr. |
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I changed the version to 2.0 and updated the code for Python 1.5 and |
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PostgreSQL 6.2.1. While I was at it I upgraded the code to use full ANSI |
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style prototypes and changed the order of arguments to connect. The latest |
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version of PyGreSQL works with PostgreSQL 7.1.3 and Python 2.1. |
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style prototypes and changed the order of arguments to connect. |
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1.2. Distribution files |
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@ -92,8 +91,7 @@ version of PyGreSQL works with PostgreSQL 7.1.3 and Python 2.1. |
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you must already have built Python as well as the mxDateTime package |
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from http://starship.python.net/~lemburg/mxDateTime.html. |
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* For Linux installation look at README.linux. If you're on an x86 system |
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that uses RPMs, then you can pick up an RPM at |
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* For a Linux x86 system that uses RPMs, you can pick up an RPM at |
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ftp://ftp.druid.net/pub/distrib/pygresql.i386.rpm |
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* Note that if you are using the DB-API module you must also install |
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@ -238,844 +236,10 @@ For support: |
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2. Programming information |
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========================== |
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You may either choose to use the old, mature interface provided by the |
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'pg' module or else the newer 'pgdb' interface compliant with DB-API 2.0 |
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specification developed by the Python DB-SIG. |
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See main PostgreSQL documentation. |
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The remainder of this chapter and the next chapter describe only |
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the older 'pg' API. As long as PyGreSQL does not contain a |
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description of the DB-API you should read about the API at |
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http://www.python.org/topics/database/DatabaseAPI-2.0.html |
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A tutorial like introduction to the DB-API can be found at |
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http://www2.linuxjournal.com/lj-issues/issue49/2605.html |
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The 'pg' module defines three objects: the pgobject that handles the connection |
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and all the requests to the database, the pglargeobject that handles |
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all the accesses to Postgres large objects and pgqueryobject that handles |
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query results. |
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If you want to see a simple example of the use of some of these functions, |
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see http://www.druid.net/rides/ where I have a link at the bottom to the |
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actual Python code for the page. |
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2.1. pg module description |
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---------------------------- |
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The module defines only a few methods that allow to connect to a database and |
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to allow to define "default variables" that override the environment variables |
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used by PostgreSQL. |
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These "default variables" were designed to allow you to handle general |
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connection parameters without heavy code in your programs. You can prompt the |
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user for a value, put it in the default variable, and forget it, without |
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having to modify your environment. The support for default variables can be |
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disabled by setting the -DNO_DEF_VAR option in the Python Setup file. Methods |
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relative to this are specified by te tag [DV]. |
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All variables are set to None at module initialization, specifying that |
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standard environment variables should be used. |
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2.1.1. connect - opens a pg connection |
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---------------------------------------- |
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Syntax: |
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connect(dbname, host, port, opt, tty, user, passwd) |
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Parameters: |
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dbname - name of connected database (string/None) |
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host - name of the server host (string/None) |
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port - port used by the database server (integer/-1) |
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opt - connection options (string/None) |
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tty - debug terminal (string/None) |
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user - PostgreSQL user (string/None) |
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passwd - password for user (string/None) |
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Return type: |
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pgobject - the object handling the connection |
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Exceptions raised: |
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TypeError - bad argument type, or too many arguments |
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SyntaxError - duplicate argument definition |
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pg.error - some error occurred during pg connection definition |
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(+ all exceptions relative to object allocation) |
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Description: |
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This method opens a connection to a specified database on a given |
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PostgreSQL server. You can use keywords here, as described in the |
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Python tutorial; |
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the names of the keywords are the name of the parameters given in the |
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syntax line. For a precise description of the parameters, please refer to |
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the PostgreSQL user manual. |
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2.1.2. get_defhost, set_defhost - default server host name handling [DV] |
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------------------------------------------------------------------------ |
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Syntax: get_defhost() |
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Parameters: |
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none |
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Return type: |
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string, None - default host specification |
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Exceptions raised: |
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SyntaxError - too many arguments |
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Description: |
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This method returns the current default host specification, or None if the |
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environment variables should be used. Environment variables won't be looked |
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up. |
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Syntax: set_defhost(host) |
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Parameters: |
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host - new default host (string/None) |
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Return type: |
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string, None - previous default host specification |
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Exceptions raised: |
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TypeError - bad argument type, or too many arguments |
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Description: |
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This methods sets the default host value for new connections. If None is |
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supplied as parameter, environment variables will be used in future |
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connections. It returns the previous setting for default host. |
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2.1.3. get_defport, set_defport - default server port handling [DV] |
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------------------------------------------------------------------- |
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Syntax: get_defport() |
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Parameters: none |
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Return type: |
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integer, None - default port specification |
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Exceptions raised: |
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SyntaxError - too many arguments |
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Description: |
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This method returns the current default port specification, or None if |
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the environment variables should be used. Environment variables won't |
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be looked up. |
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Syntax: set_defport(port) |
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Parameters: |
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port - new default port (integer/-1) |
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Return type: |
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integer, None - previous default port specification |
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Description: |
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This methods sets the default port value for new connections. If -1 is |
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supplied as parameter, environment variables will be used in future |
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connections. It returns the previous setting for default port. |
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2.1.4. get_defopt, set_defopt - default connection options handling [DV] |
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------------------------------------------------------------------------ |
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Syntax: get_defopt() |
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Parameters: none |
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Return type: |
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string, None - default options specification |
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Exceptions raised: |
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SyntaxError - too many arguments |
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Description: |
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This method returns the current default connection options specification, |
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or None if the environment variables should be used. Environment variables |
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won't be looked up. |
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Syntax: set_defopt(options) |
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Parameters: |
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options - new default connection options (string/None) |
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Return type: |
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string, None - previous default options specification |
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Exceptions raised: |
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TypeError - bad argument type, or too many arguments |
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Description: |
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This methods sets the default connection options value for new connections. |
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If None is supplied as parameter, environment variables will be used in |
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future connections. It returns the previous setting for default options. |
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2.1.5. get_deftty, set_deftty - default connection debug tty handling [DV] |
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-------------------------------------------------------------------------- |
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Syntax: get_deftty() |
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Parameters: none |
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Return type: |
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string, None - default debug terminal specification |
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Exceptions raised: |
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SyntaxError - too many arguments |
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Description: |
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This method returns the current default debug terminal specification, or |
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None if the environment variables should be used. Environment variables |
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won't be looked up. |
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Syntax: set_deftty(terminal) |
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Parameters: |
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terminal - new default debug terminal (string/None) |
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Return type: |
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string, None - previous default debug terminal specification |
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Exceptions raised: |
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TypeError - bad argument type, or too many arguments |
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Description: |
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This methods sets the default debug terminal value for new connections. If |
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None is supplied as parameter, environment variables will be used in future |
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connections. It returns the previous setting for default terminal. |
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2.1.6. get_defbase, set_defbase - default database name handling [DV] |
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--------------------------------------------------------------------- |
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Syntax: get_defbase() |
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Parameters: none |
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Return type: |
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string, None - default database name specification |
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Exceptions raised: |
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SyntaxError - too many arguments |
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Description: |
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This method returns the current default database name specification, or |
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None if the environment variables should be used. Environment variables |
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won't be looked up. |
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Syntax: set_defbase(base) |
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Parameters: |
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base - new default base name (string/None) |
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Return type: |
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string, None - previous default database name specification |
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Exceptions raised: |
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TypeError - bad argument type, or too many arguments |
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Description: |
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This method sets the default database name value for new connections. If |
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None is supplied as parameter, environment variables will be used in |
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future connections. It returns the previous setting for default host. |
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2.1.7. Module constants |
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----------------------- |
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Some constants are defined in the module dictionary. They are intended to be |
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used as parameters for methods calls. You should refer to PostgreSQL user |
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manual for more information about them. These constants are: |
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- large objects access modes, used by (pgobject.)locreate and |
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(pglarge.)open: (pg.)INV_READ, (pg.)INV_WRITE |
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- positional flags, used by (pglarge.)seek: (pg.)SEEK_SET, |
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(pg.)SEEK_CUR, (pg.)SEEK_END. |
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- version and __version__ constants that give the current version. |
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2.1.9. |
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2.1.10. Miscellaneous attributes |
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The following methods return information about the current connection. |
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- |
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2.2. pgobject description |
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--------------------------- |
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This object handle a connection to a PostgreSQL database. It embeds and |
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hides all the parameters that define this connection, thus just leaving really |
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significant parameters in function calls. |
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Some methods give direct access to the connection socket. They are specified |
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by the tag [DA]. DO NOT USE THEM UNLESS YOU REALLY KNOW WHAT YOU ARE DOING. If |
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you prefer disabling them, set the -DNO_DIRECT option in the Python Setup file. |
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Some other methods give access to large objects (refer to PostgreSQL user |
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manual for more information about these). if you want to forbid access to these |
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from the module, set the -DNO_LARGE option in the Python Setup file. These |
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methods are specified by the tag [LO]. |
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2.2.1. query - executes a SQL command string |
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-------------------------------------------- |
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Syntax: query(command) |
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Parameters: |
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command - SQL command (string) |
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Return type: |
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pgqueryobject, None - result values |
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Exceptions raised: |
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TypeError - bad argument type, or too many arguments. |
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ValueError - empty SQL query |
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pg.error - error during query processing, or invalid connection |
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Description: |
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This method simply sends a SQL query to the database. If the query is |
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an insert statement, the return value is the OID of the newly |
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inserted row. If it is otherwise a query that does not return a result |
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(ie. is not a some kind of SELECT statement), it returns None. |
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Otherwise, it returns a pgqueryobject that can be accessed via the |
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getresult or dictresult method or simply printed. |
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pgqueryobject methods |
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--------------------- |
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2.2.1.1. getresult - gets the values returned by the query |
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------------------------------------------------------------- |
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Syntax: getresult() |
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Parameters: none |
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Return type: |
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list - result values |
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Exceptions raised: |
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SyntaxError - too many parameters |
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pg.error - invalid previous result |
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Description: |
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This method returns the list of the values returned by the query. |
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More information about this result may be accessed using listfields, |
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fieldname and fieldnum methods. |
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2.2.1.2. dictresult - like getresult but returns list of dictionaries |
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--------------------------------------------------------------------- |
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Syntax: dictresult() |
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Parameters: none |
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Return type: |
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list - result values as a dictionary |
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Exceptions raised: |
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SyntaxError - too many parameters |
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pg.error - invalid previous result |
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Description: |
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This method returns the list of the values returned by the query |
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with each tuple returned as a dictionary with the field names |
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used as the dictionary index. |
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2.2.1.3. listfields - lists the fields names of the previous query result |
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----------------------------------------------------------------------- |
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Syntax: listfields() |
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Parameters: none |
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Return type: |
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list - fields names |
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Exceptions raised: |
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SyntaxError - too many parameters |
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pg.error - invalid previous result, or invalid connection |
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Description: |
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This method returns the list of names of the fields defined for the |
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query result. The fields are in the same order as the result values. |
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2.2.1.4. fieldname, fieldnum - field name-number conversion |
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--------------------------------------------------------- |
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Syntax: fieldname(i) |
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Parameters: |
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i - field number (integer) |
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Return type: |
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string - field name |
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Exceptions raised: |
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TypeError - bad parameter type, or too many parameters |
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ValueError - invalid field number |
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pg.error - invalid previous result, or invalid connection |
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Description: |
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This method allows to find a field name from its rank number. It can be |
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useful for displaying a result. The fields are in the same order as the |
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result values. |
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Syntax: fieldnum(name) |
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Parameters: |
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name - field name (string) |
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Return type: |
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integer - field number |
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Exceptions raised: |
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TypeError - bad parameter type, or too many parameters |
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ValueError - unknown field name |
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pg.error - invalid previous result, or invalid connection |
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Description: |
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This method returns a field number from its name. It can be used to |
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build a function that converts result list strings to their correct |
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type, using a hardcoded table definition. The number returned is the |
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field rank in the result values list. |
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2.2.1.5 ntuples - return number of tuples in query object |
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--------------------------------------------------------- |
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Syntax: ntuples() |
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Parameters: None |
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|
|
Return type: integer |
|
|
|
|
Description: |
|
|
|
|
This method returns the number of tuples found in a query. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2.2.2. reset - resets the connection |
|
|
|
|
------------------------------------ |
|
|
|
|
|
|
|
|
|
Syntax: reset() |
|
|
|
|
Parameters: None |
|
|
|
|
Return type: None |
|
|
|
|
Exceptions raised: |
|
|
|
|
TypeError - too many (any) arguments |
|
|
|
|
Description: |
|
|
|
|
This method resets the current database. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2.2.3. close - close the database connection |
|
|
|
|
-------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: close() |
|
|
|
|
Parameters: none |
|
|
|
|
Return type: None |
|
|
|
|
Exceptions raised: |
|
|
|
|
TypeError - too many (any) arguments |
|
|
|
|
Description: |
|
|
|
|
This method closes the database connection. The connection will |
|
|
|
|
be closed in any case when the connection is deleted but this |
|
|
|
|
allows you to explicitly close it. It is mainly here to allow |
|
|
|
|
the DB-SIG API wrapper to implement a close function. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2.2.4. fileno - returns the socket used to connect to the database |
|
|
|
|
------------------------------------------------------------------ |
|
|
|
|
|
|
|
|
|
Syntax: fileno() |
|
|
|
|
Parameters: none |
|
|
|
|
Exceptions raised: |
|
|
|
|
TypeError - too many (any) arguments |
|
|
|
|
Description: |
|
|
|
|
This method returns the underlying socket id used to connect |
|
|
|
|
to the database. This is useful for use in select calls, etc. |
|
|
|
|
Note: This function depends on having a recent version of the |
|
|
|
|
database. See "-DNO_PQSOCKET" described above. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2.2.5. getnotify - gets the last notify from the server |
|
|
|
|
------------------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: getnotify() |
|
|
|
|
Parameters: none |
|
|
|
|
Return type: |
|
|
|
|
tuple, None - last notify from server |
|
|
|
|
Exceptions raised: |
|
|
|
|
SyntaxError - too many parameters |
|
|
|
|
pg.error - invalid connection |
|
|
|
|
Description: |
|
|
|
|
This methods try to get a notify from the server (from the SQL statement |
|
|
|
|
NOTIFY). If the server returns no notify, the methods returns None. |
|
|
|
|
Otherwise, it returns a tuple (couple) (relname, pid), where relname is the |
|
|
|
|
name of the notify and pid the process id of the connection that triggered |
|
|
|
|
the notify. Remember to do a listen query first otherwise getnotify |
|
|
|
|
will always return None. |
|
|
|
|
|
|
|
|
|
2.2.6. inserttable - insert a list into a table |
|
|
|
|
----------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: inserttable(table, values) |
|
|
|
|
Parameters: |
|
|
|
|
table - the table name (string) |
|
|
|
|
values - list of rows values (list) |
|
|
|
|
Return type: |
|
|
|
|
None |
|
|
|
|
Exception raised: |
|
|
|
|
pg.error - invalid connection |
|
|
|
|
TypeError - bad argument type, or too many arguments |
|
|
|
|
Description: |
|
|
|
|
This method allow to quickly insert large blocks of data in a table: it |
|
|
|
|
inserts the whole values list into the given table. The list is a list of |
|
|
|
|
tuples/lists that define the values for each inserted row. The rows values |
|
|
|
|
may contain string, integer, long or double (real) values. |
|
|
|
|
BE VERY CAREFUL: this method doesn't typecheck the fields according to the |
|
|
|
|
table definition; it just look whether or not it knows how to handle such |
|
|
|
|
types. |
|
|
|
|
|
|
|
|
|
2.2.7. putline - writes a line to the server socket [DA] |
|
|
|
|
-------------------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: putline(line) |
|
|
|
|
Parameters: |
|
|
|
|
line - line to be written (string) |
|
|
|
|
Return type: |
|
|
|
|
None |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection |
|
|
|
|
TypeError - bad parameter type, or too many parameters |
|
|
|
|
Description: |
|
|
|
|
This method allows to directly write a string to the server socket. |
|
|
|
|
|
|
|
|
|
2.2.8. getline - gets a line from server socket [DA] |
|
|
|
|
---------------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: getline() |
|
|
|
|
Parameters: none |
|
|
|
|
Return type: |
|
|
|
|
string - the line read |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection |
|
|
|
|
SyntaxError - too many parameters |
|
|
|
|
Description: |
|
|
|
|
This method allows to directly read a string from the server socket. |
|
|
|
|
|
|
|
|
|
2.2.9. endcopy - synchronizes client and server [DA] |
|
|
|
|
---------------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: endcopy() |
|
|
|
|
Parameters: none |
|
|
|
|
Return type: |
|
|
|
|
None |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection |
|
|
|
|
SyntaxError - too many parameters |
|
|
|
|
Description: |
|
|
|
|
The use of direct access methods may desynchonize client and server. This |
|
|
|
|
method ensure that client and server will be synchronized. |
|
|
|
|
|
|
|
|
|
2.2.10. locreate - creates of large object in the database [LO] |
|
|
|
|
--------------------------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: locreate(mode) |
|
|
|
|
Parameters: |
|
|
|
|
mode - large object create mode |
|
|
|
|
Return type: |
|
|
|
|
pglarge - object handling the postgres large object |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection, or creation error |
|
|
|
|
TypeError - bad parameter type, or too many parameters |
|
|
|
|
Description: |
|
|
|
|
This method creates a large object in the database. The mode can be defined |
|
|
|
|
by OR-ing the constants defined in the pg module (INV_READ, INV_WRITE and |
|
|
|
|
INV_ARCHIVE). Please refer to PostgreSQL user manual for a description of |
|
|
|
|
the mode values. |
|
|
|
|
|
|
|
|
|
2.2.11. getlo - builds a large object from given oid [LO] |
|
|
|
|
--------------------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: getlo(oid) |
|
|
|
|
Parameters: |
|
|
|
|
oid - oid of the existing large object (integer) |
|
|
|
|
Return type: |
|
|
|
|
pglarge - object handling the postgres large object |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection |
|
|
|
|
TypeError - bad parameter type, or too many parameters |
|
|
|
|
ValueError - bad oid value (0 is invalid_oid) |
|
|
|
|
Description: |
|
|
|
|
This method allows to reuse a formerly created large object through the |
|
|
|
|
pglarge interface, providing the user have its oid. |
|
|
|
|
|
|
|
|
|
2.2.12. loimport - import a file to a postgres large object [LO] |
|
|
|
|
---------------------------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: loimport(name) |
|
|
|
|
Parameters: |
|
|
|
|
name - the name of the file to be imported (string) |
|
|
|
|
Return type: |
|
|
|
|
pglarge - object handling the postgres large object |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection, or error during file import |
|
|
|
|
TypeError - bad argument type, or too many arguments |
|
|
|
|
Description: |
|
|
|
|
This methods allows to create large objects in a very simple way. You just |
|
|
|
|
give the name of a file containing the data to be use. |
|
|
|
|
|
|
|
|
|
2.2.13. pgobject attributes |
|
|
|
|
----------------------------- |
|
|
|
|
|
|
|
|
|
Every pgobject defines a set of read-only attributes that describe the |
|
|
|
|
connection and its status. These attributes are: |
|
|
|
|
host - the hostname of the server (string) |
|
|
|
|
port - the port of the server (integer) |
|
|
|
|
db - the selected database (string) |
|
|
|
|
options - the connection options (string) |
|
|
|
|
tty - the connection debug terminal (string) |
|
|
|
|
user - the username on the database system (string) |
|
|
|
|
status - the status of the connection (integer: 1 - OK, 0 - BAD) |
|
|
|
|
error - the last warning/error message from the server (string) |
|
|
|
|
|
|
|
|
|
2.3. pglarge description |
|
|
|
|
-------------------------- |
|
|
|
|
|
|
|
|
|
This object handles all the request concerning a postgres large object. It |
|
|
|
|
embeds and hides all the 'recurrent' variables (object oid and connection), |
|
|
|
|
exactly in the same way pgobjects do, thus only keeping significant |
|
|
|
|
parameters in function calls. It keeps a reference to the pgobject used for |
|
|
|
|
its creation, sending requests though with its parameters. Any modification but |
|
|
|
|
dereferencing the pgobject will thus affect the pglarge object. |
|
|
|
|
Dereferencing the initial pgobject is not a problem since Python won't |
|
|
|
|
deallocate it before the large object dereference it. |
|
|
|
|
All functions return a generic error message on call error, whatever the |
|
|
|
|
exact error was. The 'error' attribute of the object allow to get the exact |
|
|
|
|
error message. |
|
|
|
|
|
|
|
|
|
2.3.1. open - opens a large object |
|
|
|
|
---------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: open(mode) |
|
|
|
|
Parameters: |
|
|
|
|
mode - open mode definition (integer) |
|
|
|
|
Return type: |
|
|
|
|
None |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection |
|
|
|
|
TypeError - bad parameter type, or too many parameters |
|
|
|
|
IOError - already opened object, or open error |
|
|
|
|
Description: |
|
|
|
|
This method opens a large object for reading/writing, in the same way than |
|
|
|
|
the UNIX open() function. The mode value can be obtained by OR-ing the |
|
|
|
|
constants defined in the pgmodule (INV_READ, INV_WRITE). |
|
|
|
|
|
|
|
|
|
2.3.2. close - closes a large object |
|
|
|
|
------------------------------------ |
|
|
|
|
|
|
|
|
|
Syntax: close() |
|
|
|
|
Parameters: none |
|
|
|
|
Return type: |
|
|
|
|
None |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection |
|
|
|
|
SyntaxError - too many parameters |
|
|
|
|
IOError - object is not opened, or close error |
|
|
|
|
Description: |
|
|
|
|
This method closes a previously opened large object, in the same way than |
|
|
|
|
the UNIX close() function. |
|
|
|
|
|
|
|
|
|
2.3.4. read, write, tell, seek, unlink - file like large object handling |
|
|
|
|
------------------------------------------------------------------------ |
|
|
|
|
|
|
|
|
|
Syntax: read(size) |
|
|
|
|
Parameters: |
|
|
|
|
size - maximal size of the buffer to be read |
|
|
|
|
Return type: |
|
|
|
|
sized string - the read buffer |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection or invalid object |
|
|
|
|
TypeError - bad parameter type, or too many parameters |
|
|
|
|
IOError - object is not opened, or read error |
|
|
|
|
Description: |
|
|
|
|
This function allows to read data from a large object, starting at current |
|
|
|
|
position. |
|
|
|
|
|
|
|
|
|
Syntax: write(string) |
|
|
|
|
Parameters: |
|
|
|
|
(sized) string - buffer to be written |
|
|
|
|
Return type: |
|
|
|
|
None |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection or invalid object |
|
|
|
|
TypeError - bad parameter type, or too many parameters |
|
|
|
|
IOError - object is not opened, or write error |
|
|
|
|
Description: |
|
|
|
|
This function allows to write data to a large object, starting at current |
|
|
|
|
position. |
|
|
|
|
|
|
|
|
|
Syntax: seek(offset, whence) |
|
|
|
|
Parameters: |
|
|
|
|
offset - position offset |
|
|
|
|
whence - positional parameter |
|
|
|
|
Return type: |
|
|
|
|
integer - new position in object |
|
|
|
|
Exception raised: |
|
|
|
|
pg.error - invalid connection or invalid object |
|
|
|
|
TypeError - bad parameter type, or too many parameters |
|
|
|
|
IOError - object is not opened, or seek error |
|
|
|
|
Description: |
|
|
|
|
This method allows to move the position cursor in the large object. The |
|
|
|
|
whence parameter can be obtained by OR-ing the constants defined in the |
|
|
|
|
pg module (SEEK_SET, SEEK_CUR, SEEK_END). |
|
|
|
|
|
|
|
|
|
Syntax: tell() |
|
|
|
|
Parameters: none |
|
|
|
|
Return type: |
|
|
|
|
integer - current position in large object |
|
|
|
|
Exception raised: |
|
|
|
|
pg.error - invalid connection or invalid object |
|
|
|
|
SyntaxError - too many parameters |
|
|
|
|
IOError - object is not opened, or seek error |
|
|
|
|
Description: |
|
|
|
|
This method allows to get the current position in the large object. |
|
|
|
|
|
|
|
|
|
Syntax: unlink() |
|
|
|
|
Parameter: none |
|
|
|
|
Return type: |
|
|
|
|
None |
|
|
|
|
Exception raised: |
|
|
|
|
pg.error - invalid connection or invalid object |
|
|
|
|
SyntaxError - too many parameters |
|
|
|
|
IOError - object is not closed, or unlink error |
|
|
|
|
Description: |
|
|
|
|
This methods unlinks (deletes) the postgres large object. |
|
|
|
|
|
|
|
|
|
2.3.5. size - gives the large object size |
|
|
|
|
----------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: size() |
|
|
|
|
Parameters: none |
|
|
|
|
Return type: |
|
|
|
|
integer - large object size |
|
|
|
|
Exceptions raised: |
|
|
|
|
pg.error - invalid connection or invalid object |
|
|
|
|
SyntaxError - too many parameters |
|
|
|
|
IOError - object is not opened, or seek/tell error |
|
|
|
|
Description: |
|
|
|
|
This (composite) method allows to get the size of a large object. Currently |
|
|
|
|
the large object needs to be opened. It was implemented because this |
|
|
|
|
function is very useful for a WWW interfaced database. |
|
|
|
|
|
|
|
|
|
2.3.6. export - saves a large object to a file |
|
|
|
|
---------------------------------------------- |
|
|
|
|
|
|
|
|
|
Syntax: export(name) |
|
|
|
|
Parameters: |
|
|
|
|
name - file to be created |
|
|
|
|
Return type: |
|
|
|
|
None |
|
|
|
|
Exception raised: |
|
|
|
|
pg.error - invalid connection or invalid object |
|
|
|
|
TypeError - bad parameter type, or too many parameters |
|
|
|
|
IOError - object is not closed, or export error |
|
|
|
|
Description: |
|
|
|
|
This methods allows to dump the content of a large object in a very simple |
|
|
|
|
way. The exported file is created on the host of the program, not the |
|
|
|
|
server host. |
|
|
|
|
|
|
|
|
|
2.3.7. Object attributes |
|
|
|
|
------------------------ |
|
|
|
|
|
|
|
|
|
pglarge objects define a read-only set of attributes that allow to get some |
|
|
|
|
information about it. These attributes are: |
|
|
|
|
oid - the oid associated with the object |
|
|
|
|
pgcnx - the pgobject associated with the object |
|
|
|
|
error - the last warning/error message of the connection |
|
|
|
|
BE CAREFUL: in multithreaded environments, 'error' may be modified by another |
|
|
|
|
thread using the same pgobject. Remember these object are shared, not |
|
|
|
|
duplicated. You should provide some locking to be able if you want to check |
|
|
|
|
this. |
|
|
|
|
The oid attribute is very interesting because it allow you reuse the oid |
|
|
|
|
later, creating the pglarge object with a pgobject getlo() method call. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
3. The pg wrapper |
|
|
|
|
================ |
|
|
|
|
|
|
|
|
|
The previous functions are wrapped in a module called pg. The module |
|
|
|
|
has a class called DB. The above functions are also included in the |
|
|
|
|
name space so it isn't necessary to import both modules. The preferred |
|
|
|
|
way to use this module is as follows. |
|
|
|
|
|
|
|
|
|
import pg |
|
|
|
|
db = pg.DB(...) # See description of the initialization method below. |
|
|
|
|
|
|
|
|
|
The following describes the methods and variables of this class. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
3.1. Initialization |
|
|
|
|
------------------- |
|
|
|
|
The DB class is initialized with the same arguments as the connect |
|
|
|
|
method described in section 2. It also initializes a few internal |
|
|
|
|
variables. The statement 'db = DB()' will open the local database |
|
|
|
|
with the name of the user just like connect() does. |
|
|
|
|
|
|
|
|
|
3.2. pkey |
|
|
|
|
--------- |
|
|
|
|
Syntax: |
|
|
|
|
pkey(table) |
|
|
|
|
Parameters: |
|
|
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table - name of table |
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Returns: |
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Name of field which is the primary key of the table. |
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Description: |
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This method returns the primary key of a table. Note that this raises |
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an exception if the table doesn't have a primary key. |
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3.3. get_databases - get list of databases in the system |
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-------------------------------------------------------- |
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Syntax: get_databases() |
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Parameters: none |
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Returns: list of databases in the system |
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Description: |
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Although you can do this with a simple select, it is added here for |
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convenience |
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3.4. get_tables - get list of tables in connected database |
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---------------------------------------------------------- |
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Syntax: get_tables() |
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Parameters: none |
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Returns: list of tables in connected database |
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3.5. get_attnames |
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----------------- |
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Syntax: |
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get_attnames(table) |
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Parameters: |
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table - name of table |
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Returns: |
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Dictionary of attribute names (the names are the keys, the values |
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are the names of the attributes' types) |
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Description: |
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Given the name of a table, digs out the set of attribute names. |
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3.6. get - get a tuple from a database table |
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-------------------------------------------- |
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Syntax: |
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get(table, arg, [keyname]) |
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Parameters: |
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table - name of table |
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arg - either a dictionary or the value to be looked up |
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keyname - name of field to use as key (optional) |
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Returns: |
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A dictionary mapping attribute names to row values. |
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Description: |
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This method is the basic mechanism to get a single row. It assumes |
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that the key specifies a unique row. If keyname is not specified |
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then the primary key for the table is used. If arg is a dictionary |
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then the value for the key is taken from it and it is modified to |
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include the new values, replacing existing values where necessary. |
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The oid is also put into the dictionary but in order to allow the |
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caller to work with multiple tables, the attribute name is munged |
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to make it unique. It consists of the string "oid_" followed by |
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the name of the table. |
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3.7. insert - insert a tuple into a database table |
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-------------------------------------------------- |
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Syntax: |
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insert(table, a) |
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Parameters: |
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table - name of table |
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a - a dictionary of values |
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Returns: |
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The OID of the newly inserted row. |
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Description: |
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This method inserts values into the table specified filling in the |
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values from the dictionary. It then reloads the dictionary with the |
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values from the database. This causes the dictionary to be updated |
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with values that are modified by rules, triggers, etc. |
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Due to the way that this function works you will find inserts taking |
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longer and longer as your table gets bigger. To overcome this problem |
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simply add an index onto the OID of any table that you think may get |
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large over time. |
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3.8. update |
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----------- |
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Syntax: |
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update(table, a) |
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Parameters: |
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table - name of table |
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a - a dictionary of values |
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Returns: |
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A dictionary with the new row |
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Description: |
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Similar to insert but updates an existing row. The update is based |
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on the OID value as munged by get. The array returned is the |
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one sent modified to reflect any changes caused by the update due |
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to triggers, rules, defaults, etc. |
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3.9. clear |
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---------- |
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Syntax: |
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clear(table, [a]) |
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Parameters: |
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table - name of table |
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a - a dictionary of values |
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Returns: |
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A dictionary with an empty row |
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Description: |
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This method clears all the attributes to values determined by the types. |
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Numeric types are set to 0, dates are set to 'TODAY' and everything |
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else is set to the empty string. If the array argument is present, |
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it is used as the array and any entries matching attribute names |
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are cleared with everything else left unchanged. |
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3.8. delete |
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----------- |
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Syntax: |
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delete(table, a) |
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Parameters: |
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table - name of table |
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a - a dictionary of values |
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Returns: |
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None |
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Description: |
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This method deletes the row from a table. It deletes based on the OID |
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as munged as described above. |
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4. DB-API reference |
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=================== |
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This section needs to be written. |
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5. Todo |
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3. Todo |
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======= |
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The large object and direct access functions need much more attention. |
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@ -1089,7 +253,7 @@ The DB-API module needs to be documented. |
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The fetch method should use real cursors. |
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6. Future directions |
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4. Future directions |
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==================== |
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Users should be able to register their own types with _pg. |
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