'@reify' 有什么作用，什么时候应该使用它? [英] What does '@reify' do and when should it be used?

问题描述

我在用户体验设计金字塔教程.我不太明白这个装饰器是关于什么的.

I saw it in the Pyramid tutorial for UX design. I couldn't make out much what this decorator is all about.

我看到其用法的示例代码.

Sample code where I saw its usage.

def __init__(self, request):
    self.request = request
    renderer = get_renderer("templates/global_layout.pt")
    self.global_template = renderer.implementation().macros['layout']

@reify
def company_name(self):
    return COMPANY

@reify
def site_menu(self):
    new_menu = SITE_MENU[:]
    url = self.request.url
    for menu in new_menu:
        if menu['title'] == 'Home':
            menu['current'] = url.endswith('/')
        else:
            menu['current'] = url.endswith(menu['href'])
    return new_menu

@view_config(renderer="templates/index.pt")
def index_view(self):
    return {"page_title": "Home"}

@view_config(renderer="templates/about.pt", name="about.html")
def about_view(self):
    return {"page_title": "About"}

推荐答案

来自源代码文档:

""" 放置使用此方法的结果(非数据)第一次调用后实例字典中的描述符装饰器，用实例变量有效地替换装饰器."""

""" Put the result of a method which uses this (non-data) descriptor decorator in the instance dict after the first call, effectively replacing the decorator with an instance variable."""

来自来自模糊记事本博客的描述很好地总结了它.

A description from from the fuzzy notepad blog sums it up nicely.

它的作用类似于@property，只是该函数只被调用过一次;之后，该值被缓存为常规属性.这为您提供对本应成为的对象的惰性属性创建不可变.

It acts like @property, except that the function is only ever called once; after that, the value is cached as a regular attribute. This gives you lazy attribute creation on objects that are meant to be immutable.

因此，在您发布的代码中，site_menu 可以像缓存属性一样进行访问.

So in the code you posted, site_menu can be accesses like a cached property.

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