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+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>46.1. PL/Python Functions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="plpython.html" title="Chapter 46. PL/Python — Python Procedural Language" /><link rel="next" href="plpython-data.html" title="46.2. Data Values" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">46.1. PL/Python Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plpython.html" title="Chapter 46. PL/Python — Python Procedural Language">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plpython.html" title="Chapter 46. PL/Python — Python Procedural Language">Up</a></td><th width="60%" align="center">Chapter 46. PL/Python — Python Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plpython-data.html" title="46.2. Data Values">Next</a></td></tr></table><hr /></div><div class="sect1" id="PLPYTHON-FUNCS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">46.1. PL/Python Functions</h2></div></div></div><p>
+   Functions in PL/Python are declared via the
+   standard <a class="xref" href="sql-createfunction.html" title="CREATE FUNCTION"><span class="refentrytitle">CREATE FUNCTION</span></a> syntax:
+
+</p><pre class="programlisting">
+CREATE FUNCTION <em class="replaceable"><code>funcname</code></em> (<em class="replaceable"><code>argument-list</code></em>)
+  RETURNS <em class="replaceable"><code>return-type</code></em>
+AS $$
+  # PL/Python function body
+$$ LANGUAGE plpython3u;
+</pre><p>
+  </p><p>
+   The body of a function is simply a Python script. When the function
+   is called, its arguments are passed as elements of the list
+   <code class="varname">args</code>; named arguments are also passed as
+   ordinary variables to the Python script.  Use of named arguments is
+   usually more readable.  The result is returned from the Python code
+   in the usual way, with <code class="literal">return</code> or
+   <code class="literal">yield</code> (in case of a result-set statement).  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.  In a procedure,
+   the result from the Python code must be <code class="symbol">None</code> (typically
+   achieved by ending the procedure without a <code class="literal">return</code>
+   statement or by using a <code class="literal">return</code> statement without
+   argument); otherwise, an error will be raised.
+  </p><p>
+   For example, a function to return the greater of two integers can be
+   defined as:
+
+</p><pre class="programlisting">
+CREATE FUNCTION pymax (a integer, b integer)
+  RETURNS integer
+AS $$
+  if a &gt; b:
+    return a
+  return b
+$$ LANGUAGE plpython3u;
+</pre><p>
+
+   The Python code that is given as the body of the function definition
+   is transformed into a Python function. For example, the above results in:
+
+</p><pre class="programlisting">
+def __plpython_procedure_pymax_23456():
+  if a &gt; b:
+    return a
+  return b
+</pre><p>
+
+   assuming that 23456 is the OID assigned to the function by
+   <span class="productname">PostgreSQL</span>.
+  </p><p>
+   The arguments are set as global variables.  Because of the scoping
+   rules of Python, this has the subtle consequence that an argument
+   variable cannot be reassigned inside the function to the value of
+   an expression that involves the variable name itself, unless the
+   variable is redeclared as global in the block.  For example, the
+   following won't work:
+</p><pre class="programlisting">
+CREATE FUNCTION pystrip(x text)
+  RETURNS text
+AS $$
+  x = x.strip()  # error
+  return x
+$$ LANGUAGE plpython3u;
+</pre><p>
+   because assigning to <code class="varname">x</code>
+   makes <code class="varname">x</code> a local variable for the entire block,
+   and so the <code class="varname">x</code> on the right-hand side of the
+   assignment refers to a not-yet-assigned local
+   variable <code class="varname">x</code>, not the PL/Python function
+   parameter.  Using the <code class="literal">global</code> statement, this can
+   be made to work:
+</p><pre class="programlisting">
+CREATE FUNCTION pystrip(x text)
+  RETURNS text
+AS $$
+  global x
+  x = x.strip()  # ok now
+  return x
+$$ LANGUAGE plpython3u;
+</pre><p>
+   But it is advisable not to rely on this implementation detail of
+   PL/Python.  It is better to treat the function parameters as
+   read-only.
+  </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plpython.html" title="Chapter 46. PL/Python — Python Procedural Language">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plpython.html" title="Chapter 46. PL/Python — Python Procedural Language">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plpython-data.html" title="46.2. Data Values">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 46. PL/Python — Python Procedural Language </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 46.2. Data Values</td></tr></table></div></body></html>
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