TIL

def is_valid(grid, r, c, k):
    not_in_row = k not in grid[r]
    not_in_columen = k not in [grid[i][c] for i in range(len(grid))]
    not_in_grid = k not in [
        grid[i][j]
        for i in range(r // 3 * 3, r // 3 * 3 + 3)
        for j in range(c / 3 * 3, c // 3 * 3 + 3)
    ]

from itertools import islice, tee

nwise = lambda g, *, n=2: zip(*(islice(g, i, None) for i, g in enumerate(tee(g, n))))

from sys import getrecursionlimit, setrecursionlimit
from contextlib import contextmanager


@contextmanager
def morerecursion():
    prev = getrecursionlimit()
    try:
        setrecursionlimit(2 * prev)
        yield
    finally:
        setrecursionlimit(prev)

def retry(f):
    def inner(*args, **kwargs):
        for _ in range(3):
            try:
                return f(*args, **kwargs)
            except Exception:
                pass
        ...

    return inner

def fib(a=1, b=1):
    while True:
        yield a
        a, b = b, a + b

from itertools import count

for i in count(5):
    print(i)

l = ["a", "b", "c"]
print(list(zip(count(), l)))
# [(0, 'a'), (1, 'b'), (2, 'c')]

from itertools import cycle

l = [1, 2, 3, 4, 5]
names = ["rohit", "rajat"]

for o in zip(cycle(l), names):
    print(o)

from itertools import tee

l = [1, 2, 3, 4, 5]

tee(l, 2)
# [1,2,3,4,5],[1,2,3,4,5]

from itertools import pairwise

pairwise("ABCDEFG")  # --> AB BC CD DE EF FG