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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 check_async(async_, kwargs, default):
 """Return a value of 'async' in kwargs or default when async_ is None. This helper function exists for backward compatibility (See #274). It shows a warning message when 'async' in kwargs is used to note users. """

    if async_ is not None:
        return async_
    elif 'async' in kwargs:
        warnings.warn(
            '"async" attribute is deprecated. Use "async_" instead.',
            DeprecationWarning,
        )
        return kwargs.pop('async')
    else:
        return default