Check if the actual arguments include an option
        starting with the given ``prefix`` and having a value,
        e.g. ``--format=ogg`` for ``prefix="--format"``.

        :param prefix: the option prefix
        :type  prefix: Unicode string
        :param actual_arguments: if ``True``, check among actual arguments;
                                 otherwise check among formal arguments
        :rtype actual_arguments: bool
        :rtype: Unicode string or None

def has_option_with_value(self, prefix, actual_arguments=True):
        """
        Check if the actual arguments include an option
        starting with the given ``prefix`` and having a value,
        e.g. ``--format=ogg`` for ``prefix="--format"``.

        :param prefix: the option prefix
        :type  prefix: Unicode string
        :param actual_arguments: if ``True``, check among actual arguments;
                                 otherwise check among formal arguments
        :rtype actual_arguments: bool
        :rtype: Unicode string or None
        """
        if actual_arguments:
            args = self.actual_arguments
        else:
            args = self.formal_arguments
        for arg in [arg for arg in args if (arg is not None) and (arg.startswith(prefix + u"="))]:
            lis = arg.split(u"=")
            if len(lis) >= 2:
                return u"=".join(lis[1:])
        return None