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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 set_scm(scm):
 """Sets the pants Scm."""

  if scm is not None:
    if not isinstance(scm, Scm):
      raise ValueError('The scm must be an instance of Scm, given {}'.format(scm))
    global _SCM
    _SCM = scm