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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 content_type(self) -> str: """The value of content part for Content-Type HTTP header."""

        raw = self._headers.get(hdrs.CONTENT_TYPE)  # type: ignore
        if self._stored_content_type != raw:
            self._parse_content_type(raw)
        return self._content_type