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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 next_doc_with_tag(self, doc_tag):
 """ Returns the next document with the specified tag. Empty string is no doc is found. """

        while True:
            try:
                doc = next(self)
                if doc.tag == doc_tag:
                    return doc

            except StopIteration:
                raise