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<title>Chapter39.PL/Python - Python Procedural Language</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="chapter" lang="en" id="plpython">
<div class="titlepage"><div><div><h2 class="title">
<a name="plpython"></a>Chapter39.PL/Python - Python Procedural Language</h2></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt><span class="sect1"><a href="plpython.html#plpython-funcs">39.1. PL/Python Functions</a></span></dt>
<dt><span class="sect1"><a href="plpython-trigger.html">39.2. Trigger Functions</a></span></dt>
<dt><span class="sect1"><a href="plpython-database.html">39.3. Database Access</a></span></dt>
</dl>
</div>
<a name="id732939"></a><a name="id732949"></a><p> The <span class="application">PL/Python</span> procedural language allows
<span class="productname">PostgreSQL</span> functions to be written in the
<a href="http://www.python.org" target="_top">Python language</a>.
</p>
<p> To install PL/Python in a particular database, use
<code class="literal">createlang plpythonu <em class="replaceable"><code>dbname</code></em></code>.
</p>
<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Tip</h3>
<p> If a language is installed into <code class="literal">template1</code>, all subsequently
created databases will have the language installed automatically.
</p>
</div>
<p> As of <span class="productname">PostgreSQL</span> 7.4, PL/Python is only
available as an “<span class="quote">untrusted</span>” language (meaning it does not
offer any way of restricting what users can do in it). It has
therefore been renamed to <code class="literal">plpythonu</code>. The trusted
variant <code class="literal">plpython</code> may become available again in future,
if a new secure execution mechanism is developed in Python.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p> Users of source packages must specially enable the build of
PL/Python during the installation process. (Refer to the
installation instructions for more information.) Users of binary
packages might find PL/Python in a separate subpackage.
</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="plpython-funcs"></a>39.1.PL/Python Functions</h2></div></div></div>
<p> Functions in PL/Python are declared via the usual <a href="sql-createfunction.html">CREATE FUNCTION</a>
syntax. For example:
</p>
<pre class="programlisting">CREATE FUNCTION myfunc(text) RETURNS text
AS 'return args[0]'
LANGUAGE plpythonu;</pre>
<p>
The Python code that is given as the body of the function definition
gets transformed into a Python function.
For example, the above results in
</p>
<pre class="programlisting">def __plpython_procedure_myfunc_23456():
return args[0]</pre>
<p>
assuming that 23456 is the OID assigned to the function by
<span class="productname">PostgreSQL</span>.
</p>
<p> If you do not provide a return value, Python returns the default
<code class="symbol">None</code>. <span class="application">PL/Python</span> translates
Python's <code class="symbol">None</code> into the SQL null
value.<a name="id733116"></a>
</p>
<p> The <span class="productname">PostgreSQL</span> function parameters are available in
the global <code class="varname">args</code> list. In the
<code class="function">myfunc</code> example, <code class="varname">args[0]</code> contains
whatever was passed in as the text argument. For
<code class="literal">myfunc2(text, integer)</code>, <code class="varname">args[0]</code>
would contain the <code class="type">text</code> argument and
<code class="varname">args[1]</code> the <code class="type">integer</code> argument.
</p>
<p> The global dictionary <code class="varname">SD</code> is available to store
data between function calls. This variable is private static data.
The global dictionary <code class="varname">GD</code> is public data,
available to all Python functions within a session. Use with
care.<a name="id733193"></a>
</p>
<p> Each function gets its own execution environment in the
Python interpreter, so that global data and function arguments from
<code class="function">myfunc</code> are not available to
<code class="function">myfunc2</code>. The exception is the data in the
<code class="varname">GD</code> dictionary, as mentioned above.
</p>
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