def cnv_length(attribute, arg, element):
 global pattern_length
 if (not pattern_length.match(arg)):
  raise ValueError(("'%s' is not a valid length" % arg))
 return arg

def cnv_length ( attribute , arg , element ) : global pattern_length if ( not pattern_length . match ( arg ) ) : raise ValueError ( ( "'%s' is not a valid length" % arg ) ) return arg
a physical length .