Project Euler Problem 2 in Python - Even Fibonacci Numbers (Generators, Recursion, Memoization)

Solving Problem 2 of Project Euler in Python with 2 implementations: (i) Generators; and (ii) Memoized recursive function.

Timestamps:
01:08 Generators
02:55 Recursion + Memoization

Notes:
On the inefficiency of the fib function without memoization - an illustration:
fib(100) would call fib(98), which would then call fib(96) so on and so forth, until it reaches the base case of fib(x) where x is less than 2. Each nested call, such as fib(98) and fib(96) above, would also have to evaluate all their nested calls in order to generate an answer.

With memoization:
The memoized fib function "remembers" that it has received a certain argument before, and would simply return the value, rather than going through the whole chain of nested calls.

Let me know if you have any questions!