Abnormal situation of converting "mpz" to "str" about gmpy HOT 4 CLOSED

def chudnovsky_binsplit_mpz(digits:int):
    # Use just the next line only to use gmpy2.
    from gmpy2 import mpz, isqrt

    # Comment out the previous line and uncomment the following lines
    # to use native Python. Limited to 10_000_000 digits.

    # from math import isqrt
    # import sys
    # sys.set_int_max_str_digits(10_000_100)
    # mpz = int

    digits *= 2
    def binsplit(a, b):
        if b - a == 1:
            if a == 0:
                Pab = Qab = 1
            else:
                Pab = (6*a-5) * (2*a-1) * (6*a-1)
                Qab = 640320**3//24 * a**3
            Tab = (13591409 + 545140134 * a) * Pab
            if a & 1:
                Tab = -Tab
            return mpz(Pab), mpz(Qab), mpz(Tab)
        else:
            m = (a + b) // 2
            Pam, Qam, Tam = binsplit(a, m)
            Pmb, Qmb, Tmb = binsplit(m, b)
            Pab = Pam * Pmb
            Qab = Qam * Qmb
            Tab = Qmb * Tam + Pam * Tmb
            return Pab, Qab, Tab

    terms = digits // 14 + 1
    P, Q, T = binsplit(0, terms)
    # Use 'isqrt' (integer square root) instead of 'sqrt' (floating
    # point square root).
    #
    # Remove redundant 'mpz(...)' call.
    return Q * 426880 * isqrt(10005 * mpz(10)**digits) // T

def main():
    n = 10_000_000
    pi = str(chudnovsky_binsplit_mpz(n))
    # Print exactly 'n' digits.
    print(pi[:n])


if __name__ == "__main__":
    main()