Updates the config like :meth:`update` ignoring items with non-upper
        keys.

def from_mapping(self, *mapping, **kwargs):
        """Updates the config like :meth:`update` ignoring items with non-upper
        keys.
        """
        mappings = []
        if len(mapping) == 1:
            if hasattr(mapping[0], 'items'):
                mappings.append(mapping[0].items())
            else:
                mappings.append(mapping[0])
        elif len(mapping) > 1:
            raise TypeError('expected at most 1 positional argument, got %d' % len(mapping))

        mappings.append(kwargs.items())
        for mapping in mappings:
            for key, value in mapping:
                if key.isupper():
                    self[key] = value
        return True