how to install plpython?

Hi guys,

I need to install plpython language in my db.

testdb=# create language plpythonu;
ERROR: could not access file "$libdir/plpython": No such file or directory

-bash-3.2$ pwd
/usr/pgsql-9.0/lib
-bash-3.2$ ls pl*
plpgsql.so

testdb=# select * from pg_pltemplate;
tmplname | tmpltrusted | tmpldbacreate | tmplhandler |
tmplinline | tmplvalidator | tmpllibrary | tmplacl
------------+-------------+---------------+------------------------+--------------------------+-------------------+-------------------+---------
plpgsql | t | t | plpgsql_call_handler |
plpgsql_inline_handler | plpgsql_validator | $libdir/plpgsql |
pltcl | t | t | pltcl_call_handler
| | | $libdir/pltcl |
pltclu | f | f | pltclu_call_handler
| | | $libdir/pltcl |
plperl | t | t | plperl_call_handler |
plperl_inline_handler | plperl_validator | $libdir/plperl |
plperlu | f | f | plperl_call_handler |
plperl_inline_handler | plperl_validator | $libdir/plperl |
plpythonu | f | f | plpython_call_handler |
plpython_inline_handler | | $libdir/plpython |
plpython2u | f | f | plpython_call_handler |
plpython_inline_handler | | $libdir/plpython2 |
plpython3u | f | f | plpython3_call_handler |
plpython3_inline_handler | | $libdir/plpython3 |
(8 rows)

Where may I get plpython.so?