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Added more on @cached_property, refs #20870

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Daniele Procida 2013-08-08 13:16:48 +01:00 committed by Tim Graham
parent 1c4a9bd9ad
commit 7e6af9d40c
1 changed files with 18 additions and 4 deletions
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docs/ref/utils.txt
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@ -434,8 +434,9 @@ Atom1Feed
.. class:: cached_property(object) .. class:: cached_property(object)
The ``@cached_property`` decorator caches the result of a method with a The ``@cached_property`` decorator caches the result of a method with a
single ``self`` argument as a property. The cached result will persist as single ``self`` argument as a property. The cached result will persist
long as the instance does. as long as the instance does, so if the instance is passed around and the
function subsequently invoked, the cached result will be returned.
Consider a typical case, where a view might need to call a model's method Consider a typical case, where a view might need to call a model's method
to perform some computation, before placing the model instance into the to perform some computation, before placing the model instance into the
@ -455,7 +456,7 @@ Atom1Feed
# in the template: # in the template:
{% for friend in person.friends %} {% for friend in person.friends %}
``friends()`` will be called twice. Since the instance ``person`` in Here, ``friends()`` will be called twice. Since the instance ``person`` in
the view and the template are the same, ``@cached_property`` can avoid the view and the template are the same, ``@cached_property`` can avoid
that:: that::
@ -473,7 +474,20 @@ Atom1Feed
# in the view: # in the view:
if person.friends: if person.friends:
You may clear the cached result using ``del person.friends``. The cached value can be treated like an ordinary attribute of the instance::
# clear it, requiring re-computation next time it's called
del person.friends # or delattr(person, "friends")
# set a value manually, that will persist on the instance until cleared
person.friends = ["Huckleberry Finn", "Tom Sawyer"]
As well as offering potential performance advantages, ``@cached_property``
can ensure that an attribute's value does not change unexpectedly over the
life of an instance. This could occur with a method whose computation is
based on ``datetime.now()``, or simply if a change were saved to the
database by some other process in the brief interval between subsequent
invocations of a method on the same instance.
.. function:: allow_lazy(func, *resultclasses) .. function:: allow_lazy(func, *resultclasses)