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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 get_rest_api():
 """ Get the root URL for the IBM Streams REST API. """

    assert _has_local_install

    url=[]
    ok = _run_st(['geturl', '--api'], lines=url)
    if not ok:
        raise ChildProcessError('streamtool geturl')
    return url[0]