cached_property() - computed once per instance, cached as attribute
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Python 3.8 adds great descriptor to functools: cached_property. Technically all required APIs was available since python 3.6, but it is what it is.
This package is a backport of this functionality for python 3.6 and 3.7.
.. code-block:: python
from backports.cached_property import cached_property
And then python 3.8 documentation will work (because code is minimally changed):
.. class:: cached_property
Transform a method of a class into a property whose value is computed once
and then cached as a normal attribute for the life of the instance. Similar
to property
, with the addition of caching. Useful for expensive
computed properties of instances that are otherwise effectively immutable.
Example::
class DataSet:
def __init__(self, sequence_of_numbers):
self._data = sequence_of_numbers
@cached_property
def stdev(self):
return statistics.stdev(self._data)
@cached_property
def variance(self):
return statistics.variance(self._data)
.. note::
This decorator requires that the ``__dict__`` attribute on each instance
be a mutable mapping. This means it will not work with some types, such as
metaclasses (since the ``__dict__`` attributes on type instances are
read-only proxies for the class namespace), and those that specify
``__slots__`` without including ``__dict__`` as one of the defined slots
(as such classes don't provide a ``__dict__`` attribute at all).