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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 register_writer(klass):
 """ Add engine to the excel writer registry.io.excel. You must use this method to integrate with ``to_excel``. Parameters klass : ExcelWriter """

    if not callable(klass):
        raise ValueError("Can only register callables as engines")
    engine_name = klass.engine
    _writers[engine_name] = klass