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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 decode_argument(self, value: bytes, name: str = None) -> str: """Decodes an argument from the request. The argument has been percent-decoded and is now a byte string. By default, this method decodes the argument as utf-8 and returns a unicode string, but this may be overridden in subclasses. This method is used as a filter for both `get_argument()` and for values extracted from the url and passed to `get()`/`post()`/etc. The name of the argument is provided if known, but may be None (e.g. for unnamed groups in the url regex). """

        try:
            return _unicode(value)
        except UnicodeDecodeError:
            raise HTTPError(
                400, "Invalid unicode in %s: %r" % (name or "url", value[:40])
            )