Chapter 40. PL/Python - Python Procedural Language

Table of Contents
40.1. PL/Python Functions
40.2. Trigger Functions
40.3. 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.

40.1. PL/Python Functions

The Python code you write gets transformed into a Python function. E.g.,

    AS 'return args[0]'
    LANGUAGE plpythonu;

gets transformed into

def __plpython_procedure_myfunc_23456():
        return args[0]

assuming that 23456 is the OID of the function.

If you do not provide a return value, Python returns the default None. The language module 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.