def update(self, *a, **ka):
        """ If the first parameter is a string, all keys are prefixed with this
            namespace. Apart from that it works just as the usual dict.update().

            >>> c = ConfigDict()
            >>> c.update('some.namespace', key='value')
        """
        prefix = ''
        if a and isinstance(a[0], basestring):
            prefix = a[0].strip('.') + '.'
            a = a[1:]
        for key, value in dict(*a, **ka).items():
            self[prefix + key] = value