Caching class attributes in Python

Question

I\'m writing a class in python and I have an attribute that will take a relatively long time to compute, so I only want to do it once. Also, it will not be

Answer 1

You could try looking into memoization. The way it works is that if you pass in a function the same arguments, it will return the cached result. You can find more information on implementing it in python here.

Also, depending on how your code is set up (you say that it is not needed by all instances) you could try to use some sort of flyweight pattern, or lazy-loading.

Answer 2

class MemoizeTest:

      _cache = {}
      def __init__(self, a):
          if a in MemoizeTest._cache:
              self.a = MemoizeTest._cache[a]
          else:
              self.a = a**5000
              MemoizeTest._cache.update({a:self.a})

Answer 3

The dickens package (not mine) offers cachedproperty, classproperty and cachedclassproperty decorators.

To cache a class property:

from descriptors import cachedclassproperty

class MyClass:
    @cachedclassproperty
    def approx_pi(cls):
        return 22 / 7