Lambdas inside list comprehensions

Question

I wanted to have a list of lambdas that act as sort of a cache to some heavy computation and noticed this:

>>> [j() for j in [lambda:i for i in rang         


        

Answer 1

The problem is that you're not capturing the value of i on each iteration of the list comprehension, you're capturing the variable each time through.

The problem is that a closure captures variables by reference. In this case you are capturing a variable whose value changes over time (as with all loop variables), so it has a different value when you run it than when you created it.