def join_contexts(s1, s2):
 if s1:
  if s2:
   return ('%s --> %s' % (s1, s2))
  else:
   return s1
 else:
  return s2

def join_contexts ( s1 , s2 ) : if s1 : if s2 : return ( '%s --> %s' % ( s1 , s2 ) ) else : return s1 else : return s2
join two context strings .