human
Solve the following python programming problem given the following code:
def add_binding(self, * keys, **kwargs) : 
    '
        Decorator for annotating key bindings.

        :param filter: :class:`~prompt_toolkit.filters.CLIFilter` to determine
            when this key binding is active.
        :param eager: :class:`~prompt_toolkit.filters.CLIFilter` or `bool`.
            When True, ignore potential longer matches when this key binding is
            hit. E.g. when there is an active eager key binding for Ctrl-X,
            execute the handler immediately and ignore the key binding for
            Ctrl-X Ctrl-E of which it is a prefix.
        :param invalidate_ui: :class:`~prompt_toolkit.filters.CLIFilter` or
            `bool`. When True (which is the default), invalidate (redraw) the
            user interface after handling this key binding.
        ' 
    filter = to_cli_filter (kwargs.pop ('filter', True)) 
    eager = to_cli_filter (kwargs.pop ('eager', False)) 
    invalidate_ui = to_cli_filter (kwargs.pop ('invalidate_ui', True)) 
    assert (not kwargs) 
    assert keys 
    assert all ((isinstance (k, (Key, text_type)) for k in keys)), 'Key bindings should consist of Key and string (unicode) instances.' 
    def decorator(func) : 
        if (not isinstance (filter, Never)) : 
            binding = _Binding (keys, func, filter = filter, eager = eager, invalidate_ui = invalidate_ui) 
            self.key_bindings.append (binding) 
            self._keys_to_bindings [keys].append (binding) 
            for i in range (1, len (keys)) : 
                self._keys_to_bindings_suffixes [keys [: i]].append (binding) 
return func 
return self 

    
    

    Fix the buggy line: return self
assistant
#Here is Python program to fix the buggy line: return self
.

return def decorator(