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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 set_metadata(self, metadata, utf8):
 """Sets document metadata. The ``PDF_METADATA_CREATE_DATE`` and ``PDF_METADATA_MOD_DATE`` values must be in ISO-8601 format: YYYY-MM-DDThh:mm:ss. An optional timezone of the form "[+/-]hh:mm" or "Z" for UTC time can be appended. All other metadata values can be any UTF-8 string. :param metadata: the metadata item to set. :param utf8: metadata value. *New in cairo 1.16.* *New in cairocffi 0.9.* """

        cairo.cairo_pdf_surface_set_metadata(
            self._pointer, metadata, _encode_string(utf8))
        self._check_status()