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diff --git a/doc/src/sgml/html/plpython-funcs.html b/doc/src/sgml/html/plpython-funcs.html new file mode 100644 index 0000000..c5db804 --- /dev/null +++ b/doc/src/sgml/html/plpython-funcs.html @@ -0,0 +1,88 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!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>46.2. 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-python23.html" title="46.1. Python 2 vs. Python 3" /><link rel="next" href="plpython-data.html" title="46.3. Data Values" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">46.2. PL/Python Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plpython-python23.html" title="46.1. Python 2 vs. Python 3">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 14.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plpython-data.html" title="46.3. Data Values">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLPYTHON-FUNCS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">46.2. 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 plpythonu; +</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 $$ + if a > b: + return a + return b +$$ LANGUAGE plpythonu; +</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 > 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 plpythonu; +</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 plpythonu; +</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 xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plpython-python23.html" title="46.1. Python 2 vs. Python 3">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="46.3. Data Values">Next</a></td></tr><tr><td width="40%" align="left" valign="top">46.1. Python 2 vs. Python 3 </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 46.3. Data Values</td></tr></table></div></body></html>
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