update（）方法到底做了什么（假设if条件给出了一个空字典）？

Question

我不明白dict\u字典对email\u ctx字典做了什么，它是不是空的，它是否覆盖了一些数据

class EmailTemplateContext(Context):
    @staticmethod
    def make_link(path):
        return settings.MAILING_LIST_LINK_DOMAIN + path

    def __init__(self, subscriber, dict_=None, **kwargs):
        if dict_ is None:
            dict_ = {}

        email_ctx = self.common_context(subscriber)
        email_ctx.update(dict_)
        super().__init__(email_ctx, **kwargs)

    def common_context(self, subscriber):
        subscriber_pk_kwargs = {'pk': subscriber.id}
        unsubscribe_path = reverse(
            'mailing_list:unsubscribe',
            kwargs=subscriber_pk_kwargs,
        )
        return {
            'subscriber':subscriber,
            'mailing_list': subscriber.mailing_list,
            'unsubscribe_link': self.make_link(unsubscribe_path),
        }

Answer 1

email\ u ctx.update（dict\将用dict\的值更新email\ u ctx。如果dict={}，那么nothing将在email\u ctx上更新。工作原理如下：

>>> email_ctx = { 'name': 'trump', 'age': 60}
>>> dict_ = { 'country': 'USA'} 
>>> email_ctx.update(dict_)
>>> email_ctx
{'name': 'trump', 'age': 60, 'country': 'USA'}
>>> dict_3 = {'name': 'obama'}
>>> email_ctx.update(dict_3)
>>> email_ctx
{'name': 'obama', 'age': 60, 'country': 'USA'}
>>> dict_4 = {}
>>> email_ctx.update(dict_4)
>>> email_ctx
{'name': 'obama', 'age': 60, 'country': 'USA'}