def column_mapped_collection(mapping_spec):
 cols = [expression._only_column_elements(q, 'mapping_spec') for q in util.to_list(mapping_spec)]
 keyfunc = _PlainColumnGetter(cols)
 return (lambda : MappedCollection(keyfunc))

def column_mapped_collection ( mapping_spec ) : cols = [ expression . _only_column_elements ( q , 'mapping_spec' ) for q in util . to_list ( mapping_spec ) ] keyfunc = _PlainColumnGetter ( cols ) return ( lambda : MappedCollection ( keyfunc ) )
a dictionary-based collection type with column-based keying .