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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 require_single_root_target(self):
 """If a single target was specified on the cmd line, returns that target. Otherwise throws TaskError. :API: public """

    target_roots = self.context.target_roots
    if len(target_roots) == 0:
      raise TaskError('No target specified.')
    elif len(target_roots) > 1:
      raise TaskError('Multiple targets specified: {}'
                      .format(', '.join([repr(t) for t in target_roots])))
    return target_roots[0]