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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 open(safe_file):
 """Return a SentinelDataSet object."""

    if os.path.isdir(safe_file) or os.path.isfile(safe_file):
        return SentinelDataSet(safe_file)
    else:
        raise IOError("file not found: %s" % safe_file)