def enable_if(cond, true_value, false_value=None):
 if cond:
  ret = true_value
 else:
  ret = false_value
 if (ret is None):
  ret = []
 return ret

def enable_if ( cond , true_value , false_value = None ) : if cond : ret = true_value else : ret = false_value if ( ret is None ) : ret = [ ] return ret
a global function can be called in build to filter srcs/deps by target .