Arrayify.py

class Arrayify:
    def __init__(self, f):
        self.f = f
    def __getitem__(self, i):
        print("Getitem Called")
        return self.f(i)

def f(x):
    print("Computing...")
    return ((x+1)*x)//2

g = Arrayify(f)

print(f(5))

print(g[5])

nthMagicNumber.py

from math import gcd
from bisect import bisect_left
class PQ:
    def __init__(self, p, q):
        self.p, self.q = p, q
    def __getitem__(self, k):
        # Number of multiples of p or q that is in range (0, k]
        return k//self.p + k//self.q

class Solution:
    def magicNumber(self, r, p, q):
        M = PQ(p, q)
        return bisect_left(M, r, 0, p*q)

    def nthMagicalNumber(self, N, A, B):
        M = 10**9 + 7
        m = gcd(A, B)
        p, q = A//m, B//m
        n, r = divmod(N, p+q-1)
        # npq = n*p*q
        npq = (n*p*q)%M
        R = self.magicNumber(r, p, q)
        return ((npq + R)*m)%M

Padding.py

class Padding:
    def __init__(self, arr):
        self.arr = arr
    def __getitem__(self, i):
        if i < 0:
            return -inf
        elif i >= len(self.arr):
            return inf
        else:
            return self.arr[i]

a = [2,3,4,5,6]

b = Padding(a)

print(type(b))

for i in range(-3, 6):
    print(i, b[i])