I saw it in the Pyramid tutorial for UX design. I couldn't make out much what this decorator is all about.
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"}
From the source code documentation:
""" 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."""
A description from from the fuzzy notepad blog sums it up nicely.
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.
So in the code you posted, site_menu can be accesses like a cached property.