pglarge   This object handles all the request concerning a
   PostgreSQL large object. It embeds and
   hides all the "recurrent" variables (object OID and
   connection), exactly in the same way
   pgobjects do, thus only keeping significant
   parameters in function calls. It keeps a reference to the pgobject
   used for its creation, sending requests though with its
   parameters. Any modification but dereferencing the
   pgobject will thus affect the
   pglarge object.  Dereferencing the initial
   pgobject is not a problem since
   Python will not deallocate it before the
   large object dereference it.  All functions return a generic error
   message on call error, whatever the exact error was. The
   error attribute of the object allows to
   get the exact error message.
  
   pglarge objects define a read-only set of
   attributes that allow to get some information about it. These
   attributes are:
   
the OID associated with the object
       the pgobject associated with the object
      
the last warning/error message of the connection
Important: In multithreaded environments, error may be modified by another thread using the same
pgobject. Remember that these object are shared, not duplicated; you should provide some locking if you want to check for the error message in this situation. The OID attribute is very interesting because it allow you to reuse the OID later, creating thepglargeobject with apgobjectgetlo()method call.
See also Chapter 2 for more information about the PostgreSQL large object interface.