<p><code>LazyUser</code>对象是一个<a href="http://docs.python.org/2/howto/descriptor.html" rel="nofollow">Python descriptor</a>,也就是说,一个可以指定如何通过其父类的实例访问自身的对象。(那是一口)让我看看能不能给你讲讲:</p>
<pre><code># Having a LazyUser means we don't have to get the actual User object
# for each request before it's actually accessed.
class LazyUser(object):
# Define the __get__ operation for the descripted object.
# According to the docs, "descr.__get__(self, obj, type=None) > value".
# We don't need the type (obj_type) for anything, so don't mind that.
def __get__(self, request, obj_type=None):
# This particular request doesn't have a cached user?
if not hasattr(request, '_cached_user'):
# Then let's go get it!
from django.contrib.auth import get_user
# And save it to that "hidden" field.
request._cached_user = get_user(request)
# Okay, now we have it, so return it.
return request._cached_user
class AuthenticationMiddleware(object):
# This is done for every request...
def process_request(self, request):
# Sanity checking.
assert hasattr(request, 'session'), "blah blah blah."
# Put the descriptor in the class's dictionary. It can thus be
# accessed by the class's instances with `.user`, and that'll
# trigger the above __get__ method, eventually returning an User,
# AnonymousUser, or what-have-you.
# Come to think of it, this probably wouldn't have to be done
# every time, but the performance gain of checking whether we already
# have an User attribute would be negligible, or maybe even negative.
request.__class__.user = LazyUser()
# We didn't mess with the request enough to have to return a
# response, so return None.
return None
</code></pre>
<p>这有帮助吗?:)</p>