Code that can calculate almost infinity digits after comma. Works as-is, no comma sign, just a lot of numbers in a HUGE integer. Example: f(2) = 1414213562373095048801688724209698078569671875376948073176679737990732478462107038850387534327641572

squares.py

import sys
sys.set_int_max_str_digits(100000)
def square(number, amount_of_digits=100):
    s = 1
    approximate = 0
    for i in range(amount_of_digits):
        for z in range(1,number*10):
            apr10 = approximate*10
            if (apr10+z)**2 > number * 10**((s-1)*2):
                approximate = apr10 + z-1
                s += 1
                break
    return approximate
print(square(2))