Generating Pi decimals revisited

# a generator to approximate pi to n decimals
# tested with Python 2.5.4 and Python 3.1.1  by vegaseat http://www.daniweb.com/software-development/python/code/249177
# tested with Python 2.7.1 and Python 3.2 by tonyjv (line continuations removed, num_dec, str added)
def pi_generate(num_dec):
    """
    generator to approximate pi
    
    returns a single digit as character of pi each time iterated until num_dec generated
    
    """
    n, q, r, t, k, m, x = 0, 1, 0, 1, 1, 3, 3
    while True:
        if 4 * q + r - t < m * t:
            yield str(m)
            n += 1
            if n > num_dec: return
            q, r, t, k, m, x = (10 * q,
                                10 * (r - m * t),
                                t,
                                k,
                                (10 * (3 * q + r)) // t - 10 * m,
                                x)
        else:
            q, r, t, k, m, x = (q * k,
                                (2 * q + r) * x,
                                t * x,
                                k + 1,
                                (q * (7 * k + 2) + r * x)//(t * x),
                                x + 2)


# number of decimal digits desired
# used 56 here to make it display well, n can be much higher
n = 56
pi_str = ''.join(pi_generate(n))
# use string slicing to insert the missing period at index 1
pi_str = pi_str[0] + '.' + pi_str[1:]

print("""pi approx. to %d decimals (below it is published pi):
%s
3.14159265358979323846264338327950288419716939937510582097""" % (n, pi_str))