I wrote this for fun. Slow as hell. Maybe broken. Don't use.

pi_digits.py

from math import floor
from fractions import Fraction as F


def pi_approx(bits):
    def term(k):
        return F(1, 16 ** k) * (F(4, 8 * k + 1) - F(2, 8 * k + 4) - F(1, 8 * k + 5) - F(1, 8 * k + 6))

    return sum(term(k) for k in range(bits // 4 + 1))


def pi_decimal_digits(n):
    denom = 10 ** n
    p = pi_approx(denom.bit_length())

    int_part = floor(p)
    fract_part = p - int_part

    return str(int_part) + '.' + str(floor(fract_part * denom)).ljust(n, '0')


print(pi_decimal_digits(1))
print(pi_decimal_digits(2))
print(pi_decimal_digits(5))
print(pi_decimal_digits(1000))