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diff --git a/doc/src/sgml/plpython.sgml b/doc/src/sgml/plpython.sgml deleted file mode 100644 index 2e38a5c7917..00000000000 --- a/doc/src/sgml/plpython.sgml +++ /dev/null @@ -1,223 +0,0 @@ -<!-- $Header: /cvsroot/pgsql/doc/src/sgml/plpython.sgml,v 1.10 2002/03/22 19:20:18 petere Exp $ --> - -<chapter id="plpython"> - <title>PL/Python - Python Procedural Language</title> - - <indexterm zone="plpython"><primary>PL/Python</></> - <indexterm zone="plpython"><primary>Python</></> - - <sect1 id="plpython-intro"> - <title>Introduction</title> - - <para> - The <application>PL/Python</application> procedural language allows - <productname>PostgreSQL</productname> functions to be written in - the <ulink url="http://www.python.org">Python</ulink> language. - </para> - - <para> - The current version of <application>PL/Python</application> - functions as a trusted language only; access to the file system and - other local resources is disabled. Specifically, - <application>PL/Python</application> uses the Python restricted - execution environment, further restricts it to prevent the use of - the file <function>open</> call, and allows only modules from a - specific list to be imported. Presently, that list includes: - array, bisect, binascii, calendar, cmath, codecs, errno, marshal, - math, md5, mpz, operator, pcre, pickle, random, re, regex, sre, - sha, string, StringIO, struct, time, whrandom, and zlib. - </para> - - <para> - In the current version, any database error encountered while - running a <application>PL/Python</application> function will result - in the immediate termination of that function by the server. It is - not possible to trap error conditions using Python <literal>try - ... catch</literal> constructs. For example, a syntax error in an - SQL statement passed to the <literal>plpy.execute()</literal> call - will terminate the function. This behavior may be changed in a - future release. - </para> - </sect1> - - <sect1 id="plpython-install"> - <title>Installation</title> - - <para> - To build PL/Python, the <option>--with-python</option> option needs - to be specified when running <filename>configure</filename>. If - after building and installing you have a file called - <filename>plpython.so</filename> (possibly a different extension), - then everything went well. Otherwise you should have seen a notice - like this flying by: -<screen> -*** Cannot build PL/Python because libpython is not a shared library. -*** You might have to rebuild your Python installation. Refer to -*** the documentation for details. -</screen> - That means you have to rebuild (part of) your Python installation - to supply this shared library. - </para> - - <para> - The catch is that the Python distribution or the Python maintainers - do not provide any direct way to do this. The closest thing we can - offer you is the information in <ulink - url="http://www.python.org/doc/FAQ.html#3.30">Python FAQ - 3.30</ulink>. On some operating systems you don't really have to - build a shared library, but then you will have to convince the - PostgreSQL build system of this. Consult the - <filename>Makefile</filename> in the - <filename>src/pl/plpython</filename> directory for details. - </para> - </sect1> - - <sect1 id="plpython-using"> - <title>Using PL/Python</title> - - <para> - There are sample functions in - <filename>plpython_function.sql</filename>. The Python code you - write gets transformed into a function. E.g., -<programlisting> -CREATE FUNCTION myfunc(text) RETURNS text AS -'return args[0]' -LANGUAGE 'plpython'; -</programlisting> - - gets transformed into - -<programlisting> -def __plpython_procedure_myfunc_23456(): - return args[0] -</programlisting> - - where 23456 is the OID of the function. - </para> - - <para> - If you do not provide a return value, Python returns the default - <symbol>None</symbol> which may or may not be what you want. The - language module translates Python's None into SQL NULL. - </para> - - <para> - <productname>PostgreSQL</> function variables are available in the global - <varname>args</varname> list. In the <function>myfunc</function> - example, <varname>args[0]</> contains whatever was passed in as the text - argument. For <literal>myfunc2(text, integer)</literal>, <varname>args[0]</> - would contain the <type>text</type> variable and <varname>args[1]</varname> the <type>integer</type> variable. - </para> - - <para> - The global dictionary SD is available to store data between - function calls. This variable is private static data. The global - dictionary GD is public data, available to all python functions - within a backend. Use with care. - </para> - - <para> - Each function gets its own restricted execution object in the - Python interpreter, so that global data and function arguments from - <function>myfunc</function> are not available to - <function>myfunc2</function>. The exception is the data in the GD - dictionary, as mentioned above. - </para> - - <para> - When a function is used in a trigger, the dictionary TD contains - transaction related values. The trigger tuples are in <literal>TD["new"]</> - and/or <literal>TD["old"]</> depending on the trigger event. <literal>TD["event"]</> - contains the event as a string (<literal>INSERT</>, <literal>UPDATE</>, <literal>DELETE</>, or - <literal>UNKNOWN</>). TD["when"] contains one of (<literal>BEFORE</>, <literal>AFTER</>, or - <literal>UNKNOWN</>). <literal>TD["level"]</> contains one of <literal>ROW</>, <literal>STATEMENT</>, or - <literal>UNKNOWN</>. <literal>TD["name"]</> contains the trigger name, and <literal>TD["relid"]</> - contains the relation id of the table on which the trigger occurred. - If the trigger was called with arguments they are available - in <literal>TD["args"][0]</> to <literal>TD["args"][(n -1)]</>. - </para> - - <para> - If the trigger <quote>when</quote> is <literal>BEFORE</>, you may return <literal>None</literal> or <literal>"OK"</literal> - from the Python function to indicate the tuple is unmodified, - <literal>"SKIP"</> to abort the event, or <literal>"MODIFIED"</> to indicate you've - modified the tuple. - </para> - - <para> - The PL/Python language module automatically imports a Python module - called <literal>plpy</literal>. The functions and constants in - this module are available to you in the Python code as - <literal>plpy.<replaceable>foo</replaceable></literal>. At present - <literal>plpy</literal> implements the functions - <literal>plpy.debug("msg")</literal>, - <literal>plpy.log("msg")</literal>, - <literal>plpy.info("msg")</literal>, - <literal>plpy.notice("msg")</literal>, - <literal>plpy.warning("msg")</literal>, - <literal>plpy.error("msg")</literal>, and - <literal>plpy.fatal("msg")</literal>. They are mostly equivalent - to calling <literal>elog(<replaceable>LEVEL</>, "msg")</literal>. - <function>plpy.error</function> and <function>plpy.fatal</function> - actually raise a Python exception which, if uncaught, causes the - PL/Python module to call <literal>elog(ERROR, msg)</literal> when - the function handler returns from the Python interpreter. Long - jumping out of the Python interpreter is probably not good. - <literal>raise plpy.ERROR("msg")</literal> and <literal>raise - plpy.FATAL("msg")</literal> are equivalent to calling - <function>plpy.error</function> or <function>plpy.fatal</function>. - </para> - - <para> - Additionally, the <literal>plpy</literal> module provides two functions called - <function>execute</function> and <function>prepare</function>. - Calling <function>plpy.execute</function> with a query string, and - an optional limit argument, causes that query to be run, and the - result returned in a result object. The result object emulates a - list or dictionary object. The result object can be accessed by - row number, and field name. It has these additional methods: - <function>nrows()</function> which returns the number of rows - returned by the query, and <function>status</function> which is the - <function>SPI_exec</function> return variable. The result object - can be modified. - -<programlisting> -rv = plpy.execute("SELECT * FROM my_table", 5) -</programlisting> - returns up to 5 rows from my_table. Ff my_table has a column - my_field it would be accessed as -<programlisting> -foo = rv[i]["my_field"] -</programlisting> - The second function <function>plpy.prepare</function> is called - with a query string, and a list of argument types if you have bind - variables in the query. -<programlisting> -plan = plpy.prepare("SELECT last_name FROM my_users WHERE first_name = $1", [ "text" ]) -</programlisting> - text is the type of the variable you will be passing as $1. After - preparing you use the function <function>plpy.execute</function> to - run it. -<programlisting> -rv = plpy.execute(plan, [ "name" ], 5) -</programlisting> - The limit argument is optional in the call to - <function>plpy.execute</function>. - </para> - - <para> - When you prepare a plan using the PL/Python module it is - automatically saved. Read the SPI documentation (<xref - linkend="spi">) for a description of what this means. The take - home message is if you do -<programlisting> -plan = plpy.prepare("SOME QUERY") -plan = plpy.prepare("SOME OTHER QUERY") -</programlisting> - you are leaking memory, as I know of no way to free a saved plan. - The alternative of using unsaved plans it even more painful (for - me). - </para> - </sect1> - -</chapter> |