How to use the puremagic.magic_string function in puremagic

def test_string_with_confidence(self):
        """String identification: magic_string """
        ext = puremagic.magic_string(bytes(self.mp4magic))
        self.assertEqual(self.expect_ext, ext[0].extension)
        self.assertRaises(ValueError, puremagic.magic_string, "")

def test_magic_string_with_filename_hint(self):
        """String identification: magic_string with hint """
        filename = os.path.join(OFFICE_DIR, "test.xlsx")
        with open(filename, "rb") as f:
            data = f.read()
        ext = puremagic.magic_string(data, filename=filename)
        self.assertEqual(".xlsx", ext[0].extension)

def test_string_with_confidence(self):
        """String identification: magic_string """
        ext = puremagic.magic_string(bytes(self.mp4magic))
        self.assertEqual(self.expect_ext, ext[0].extension)
        self.assertRaises(ValueError, puremagic.magic_string, "")

async def get_mimetype(self):
        """Return the mimetype for the file."""
        if self._mimetype:
            return self._mimetype

        try:
            results = puremagic.magic_string(await self.get_file_bytes())
        except puremagic.PureError:
            # If no results return none
            return ""

        # If for some reason we get a len 0 list
        if not results:  # pragma: nocover
            return ""

        # If we only have one result use it.
        if len(results) == 1:  # pragma: nocover
            return results[0].mime_type

        # If we have multiple matches with the same confidence, pick one that
        # actually has a mime_type.
        confidence = results[0].confidence
        results = filter(lambda x: x.confidence == confidence, results)