PL/Python: How do I use result methods?

I'm having my first try at a PL/Python function.  It is also a first try
at Python, so the answer to this may be obvious.

According to the docs (8.0):

        Calling plpy.execute with a query string and an optional limit
        argument causes that query to be run and the result to be
        returned in a result object. The result object emulates a list
        or dictionary object. The result object can be accessed by row
        number and column name. It has these additional methods: nrows
        which returns the number of rows returned by the query, and
        status which is the SPI_execute() return value.

What exactly is the syntax for using the nrows and status methods?

I am trying to use it like this:

...
arec = plpy.execute(plan, [ addrno ], 1)
plpy.info("Executed plan")
n = plpy.nrows(arec)
plpy.info("  got nrows")
...

This gives the output:
advacs=# select core.formatted_address(1);
INFO:  ('Prepared plan',)
INFO:  ('Executed plan',)
ERROR:  plpython: function "formatted_address" failed
DETAIL:  exceptions.AttributeError: 'module' object has no attribute 'nrows'


If I use
  n = arec.nrows

the message becomes
DETAIL:  exceptions.SystemError: error return without exception set

so how do you use it?

-- 
Oliver Elphick                                          olly@xxxxxxxxxx
Isle of Wight                              http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA  92C8 39E7 280E 3631 3F0E  1EC0 5664 7A2F A543 10EA
                 ========================================
     "But be ye doers of the word, and not hearers only, 
      deceiving your own selves."              James 1:22 


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