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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 cli(env, columns):
 """List Users."""


    mgr = SoftLayer.UserManager(env.client)
    users = mgr.list_users()

    table = formatting.Table(columns.columns)
    for user in users:
        table.add_row([value or formatting.blank()
                       for value in columns.row(user)])

    env.fout(table)