Spigot algorithm for computing digits of square root

computesqrt.py

#!/usr/bin/env python3
# Adapted from https://rosettacode.org/wiki/Square_root_by_hand

def next_digit(val, k):
    for d in range(1, 11):
        if val < d * (k + d):
            return d - 1
    raise RuntimeError("Impossible")

def compute_sqrt(val=2, num_char=500):
    j = int(val**.5)
    k, d = j, j
    rc=""
    for n in range(num_char):
        rc=f"{d}." if len(rc) == 0 else f"{rc}{d}"
        val, k = 100 * (val - k * d), 20 * j
        d = next_digit(val, k)
        j, k = d + j * 10, k + d
    return rc

if __name__ == "__main__":
    print(compute_sqrt(2, 1000))