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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 file(data, response, **kwargs):
 """A dynamically retrieved file"""

    if not data:
        response.content_type = 'text/plain'
        return ''

    if hasattr(data, 'read'):
        name, data = getattr(data, 'name', ''), data
    elif os.path.isfile(data):
        name, data = data, open(data, 'rb')
    else:
        response.content_type = 'text/plain'
        response.status = HTTP_NOT_FOUND
        return 'File not found!'

    response.content_type = mimetypes.guess_type(name, None)[0] or 'application/octet-stream'
    return data