Get a list of completion candidates for the symbol at offset.

def rpc_get_completions(self, filename, source, offset):
        """Get a list of completion candidates for the symbol at offset.

        """
        results = self._call_backend("rpc_get_completions", [], filename,
                                     get_source(source), offset)
        # Uniquify by name
        results = list(dict((res['name'], res) for res in results)
                       .values())
        results.sort(key=lambda cand: _pysymbol_key(cand["name"]))
        return results