(Image from Adrian Swancar)
It's not something complex but it's very useful anyway to do not wait or stress your infrastructure... for nothing!
The idea is to have an empty attribute that will get its value only when accessed the first time. To illustrate, I used a class Gift with an attribute price that is slow to compute:
import time class Gift(): _price = None def __init__(self, what): self.what = what def costly_computation(self): print("Costly computation") time.sleep(2) return 10 @property def price(self): if not self._price: self._price = self.costly_computation() return self._price
The costly computation will only affect when accessing the attribute, and it will happen only one time (first access) 😃
>>> from gift import * >>> g = Gift("Sunglasses") >>> g.price Costly computation # ... # ... freezes a bit # ... 10 >>> g.price 10
That's all 😙