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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 doi_exists(self, doi):
 """ This method retrieve a boolean according to the existence of a crossref DOI number. It returns False if the API results a 404 status code. args: Crossref DOI id (String) return: Boolean Example 1: True Example 2: False """

        request_url = build_url_endpoint(
            '/'.join([self.ENDPOINT, doi])
        )
        request_params = {}

        result = self.do_http_request(
            'get',
            request_url,
            data=request_params,
            only_headers=True,
            custom_header=str(self.etiquette)
        )

        if result.status_code == 404:
            return False

        return True