human
Solve the following python programming problem given the following code:
def ast_walk(root, dispatcher, debug = False) : 
    'Walk the given tree and for each node apply the corresponding function
    as defined by the dispatcher.
    
    If one node type does not have any function defined for it, it simply
    returns the node unchanged.
    
    Parameters
    ----------
    root : Node
        top of the tree to walk into.
    dispatcher : Dispatcher
        defines the action for each node type.
    ' 
    def _walker(par) : 
        children = [] 
        for c in par.children : 
            children.append (_walker (c)) 
par.children = [c for c in children if (c is not None)] 
        try : 
            func = dispatcher.action_dict [par.type] 
            return func (par) 
except KeyError : 
            if debug : 
                print (('no action for type %s' % par.type)) 
return par 
return _walker (__copy (_walker)) 

    
    

    Fix the buggy line: return _walker (__copy (_walker))
assistant
#Here is Python code to fix the buggy line: return _walker (__copy (_walker))
.

return _walker (__copy (root))