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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 validate(self):
 """Validate keys and values. Check to make sure every key used is a valid Vorbis key, and that every value used is a valid Unicode or UTF-8 string. If any invalid keys or values are found, a ValueError is raised. In Python 3 all keys and values have to be a string. """


        if not isinstance(self.vendor, text_type):
            if PY3:
                raise ValueError("vendor needs to be str")

            try:
                self.vendor.decode('utf-8')
            except UnicodeDecodeError:
                raise ValueError

        for key, value in self:
            try:
                if not is_valid_key(key):
                    raise ValueError("%r is not a valid key" % key)
            except TypeError:
                raise ValueError("%r is not a valid key" % key)

            if not isinstance(value, text_type):
                if PY3:
                    err = "%r needs to be str for key %r" % (value, key)
                    raise ValueError(err)

                try:
                    value.decode("utf-8")
                except Exception:
                    err = "%r is not a valid value for key %r" % (value, key)
                    raise ValueError(err)

        return True