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Chapter 39. PL/Python - Python Procedural Language

Table of Contents
39.1. PL/Python Functions
39.2. Trigger Functions
39.3. Database Access

The PL/Python procedural language allows PostgreSQL functions to be written in the Python language.

To install PL/Python in a particular database, use createlang plpythonu dbname.

Tip: If a language is installed into template1, all subsequently created databases will have the language installed automatically.

As of PostgreSQL 7.4, PL/Python is only available as an "untrusted" language (meaning it does not offer any way of restricting what users can do in it). It has therefore been renamed to plpythonu. The trusted variant plpython may become available again in future, if a new secure execution mechanism is developed in Python.

Note: 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.

39.1. PL/Python Functions

Functions in PL/Python are declared via the usual CREATE FUNCTION syntax. For example:

CREATE FUNCTION myfunc(text) RETURNS text
    AS 'return args[0]'
    LANGUAGE plpythonu;

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

def __plpython_procedure_myfunc_23456():
        return args[0]

assuming that 23456 is the OID assigned to the function by PostgreSQL.

If you do not provide a return value, Python returns the default None. PL/Python translates Python's None into the SQL null value.

The PostgreSQL function parameters are available in the global args list. In the myfunc example, args[0] contains whatever was passed in as the text argument. For myfunc2(text, integer), args[0] would contain the text argument and args[1] the integer argument.

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 session. Use with care.

Each function gets its own execution environment in the Python interpreter, so that global data and function arguments from myfunc are not available to myfunc2. The exception is the data in the GD dictionary, as mentioned above.

Comments


July 3, 2006, 3:58 p.m.

Ought to mention that plpythonu can't return tuples.


July 15, 2006, 7:10 p.m.

An ugly workaround to return sets from python is passing throught plperl for example:

CREATE OR REPLACE FUNCTION perl_set_int(text /* comma separated */)
RETURNS SETOF INTEGER AS $$
return [split(/,/, $_[0])];
$$ LANGUAGE plperl;

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