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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 is_namespace_valid( namespace_id ):
 """ Is a namespace ID valid? True False False False False True """

    if not is_b40( namespace_id ) or "+" in namespace_id or namespace_id.count(".") > 0:
        return False

    if len(namespace_id) == 0 or len(namespace_id) > LENGTHS['blockchain_id_namespace_id']:
        return False

    return True