参见`werkzeug.datastructures`模块中的`Header`类的`extend`方法， 参数可以是`dict`，`list`，或者`iterable yielding keys and values`：
```
    def extend(self, iterable):
        """Extend the headers with a dict or an iterable yielding keys and
        values.
        """
        if isinstance(iterable, dict):
            for key, value in iteritems(iterable):
                if isinstance(value, (tuple, list)):
                    for v in value:
                        self.add(key, v)
                else:
                    self.add(key, value)
        else:
            for key, value in iterable:
                self.add(key, value)
```