code: def changed(self, src, path, dest):
          
          try:
              mtime = os.path.getmtime(os.path.join(src, path))
              self._build(src, path, dest, mtime)
          except EnvironmentError as e:
              logging.error("{0} is inaccessible: {1}".format(
                  termcolor.colored(path, "yellow", attrs=["bold"]),
                  e.args[0]
              ))
docs: Called whenever `path` is changed in the source folder `src`. `dest`
          is the output folder. The default implementation calls `build` after
          determining that the input file is newer than any of the outputs, or
          any of the outputs does not exist.