Chudnovsky formula

pi.py

from math import factorial
from gmpy2 import mpz, mpq, get_context


def pi(iterations):
    result = mpq()
    for k in range(iterations):
        num = mpz(factorial(6*k)*(13591409+545140134*k))
        den = mpz(factorial(3*k)*factorial(k)**3*(-640320)**(3*k))
        result += mpq(num, den)
    return mpq(640320)**mpq(3, 2) * mpq(1, result * mpq(12))

get_context().precision = 3500
print(str(pi(75))[:1001])