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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def path(self, root_dir):
 """Manually establishes the build root for the current workspace."""

    path = os.path.realpath(root_dir)
    if not os.path.exists(path):
      raise ValueError('Build root does not exist: {}'.format(root_dir))
    self._root_dir = path