``q`` will use ``nbits/2`` bits.
    :param getprime_func: either :py:func:`rsa.prime.getprime` or a function
        with similar signature.
    :param exponent: the exponent for the key; only change this if you know
        what you're doing, as the exponent influences how difficult your
        private key can be cracked. A very common choice for e is 65537.
    :type exponent: int
    TrL