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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 get_span_kind_as_int(self, span):
 """ Will retrieve the `span.kind` tag and return the appropriate integer value for the Instana backend or None if the tag is set to something we don't recognize. :param span: The span to search for the `span.kind` tag :return: Integer """

        kind = None
        if "span.kind" in span.tags:
            if span.tags["span.kind"] in self.entry_kind:
                kind = 1
            elif span.tags["span.kind"] in self.exit_kind:
                kind = 2
            else:
                kind = 3
        return kind