CODEWITHSUNDEEP
pythonpropertiesclass-method
Eduardo
Eduardo

Reputation: 701

Calculate property only once and use the result several times (different approaches)

I'm trying to use the result of a class method several times without doing the heavy calculations required to obtain the result.

I am seeing the following options. Which ones do you think is the right one, or more pythonic?

What are the advantages and disadvantages of each one?

Try/Except approach

class Test:
    def __init__(self, *args):
        # do stuff

    @property
    def new_method(self):
        try:
            return self._new_property
        except AttributeError:
            # do some heavy calculations
            return self._new_property

lru_cache approach

from functools import lru_cache

class Test:
    def __init__(self, *args):
        # do stuff

    @property
    @lru_cache()
    def new_method(self):
        # do some heavy calculations
        return self._new_property

Django's cache_property approach

from django.utils.functional import cached_property

class Test:
    def __init__(self, *args):
        # do stuff

    @cached_property
    def new_method(self):
        # do some heavy calculations
        return self._new_property

Upvotes: 14

Views: 3411

Answers (2)

Martin Thoma
Martin Thoma

Reputation: 136347

Python 3.8 update: You can now use functools.cached_property

from functools import cached_property

class Test:
    def __init__(self, *args):
        # do stuff

    @cached_property
    def new_method(self):
        # do some heavy calculations
        return self._new_property

Upvotes: 14

Alex Pertsev
Alex Pertsev

Reputation: 948

  1. Try/except is simple and readable, but one day you would want to cache another property, right? So one day you will write your own cached property probably.

  2. lru_cache it is a good idea to use standard library, but as you don't need lru cache, it is an overhead probably.

  3. Django's cache_property works exactly as you want and it is pretty simple. It has analogue in werkzeug (so Flask users familiar with it too), it is easy to find a sources, so probably it is a good choice for you.

Upvotes: 4

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