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.
Functions in PL/Python are declared via the usual CREATE FUNCTION syntax. For example:
CREATE FUNCTION myfunc(text) RETURNS text AS 'return args' 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
assuming that 23456 is the OID assigned to the function by PostgreSQL.
The PostgreSQL function parameters are available in
the global args list. In the
myfunc example, args contains
whatever was passed in as the text argument. For
myfunc2(text, integer), args
would contain the text argument and
args 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.