Forbidden Python

fibdict.py

class Fib(dict):
    def __init__(self):
        self[0] = self[1] = 1

    def __missing__(self, k):
        fibk = self[k] = self[k - 1] + self[k - 2]
        return fibk

fib = Fib()
print(fib[10])
print(fib[100])
print(fib[200])
print(len(fib))

# 89
# 573147844013817084101
# 453973694165307953197296969697410619233826
# 201