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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 parse(self, rrstr):
        # type: (bytes) -> None
        '''
        Parse a Rock Ridge Alternate Name record out of a string.

        Parameters:
         rrstr - The string to parse the record out of.
        Returns:
         Nothing.
        '''
        if self._initialized:
            raise pycdlibexception.PyCdlibInternalError('NM record already initialized!')

        (su_len, su_entry_version_unused, self.posix_name_flags) = struct.unpack_from('=BBB', rrstr[:5], 2)

        # We assume that the caller has already checked the su_entry_version,
        # so we don't bother.

        name_len = su_len - 5
        if (self.posix_name_flags & 0x7) not in (0, 1, 2, 4):
            raise pycdlibexception.PyCdlibInvalidISO('Invalid Rock Ridge NM flags')

        if name_len != 0:
            if (self.posix_name_flags & (1 << 1)) or (self.posix_name_flags & (1 << 2)) or (self.posix_name_flags & (1 << 5)):
                raise pycdlibexception.PyCdlibInvalidISO('Invalid name in Rock Ridge NM entry (0x%x %d)' % (self.posix_name_flags, name_len))
            self.posix_name += rrstr[5:5 + name_len]

        self._initialized = True