Table of Contents
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
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.
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[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.