Calculate e (euler's number), as long as you want

euler.py

length = 50
n = 2
first_numerator = 3
first_denominator = 1
second_numerator = 8
second_denominator = 3

result = []
for i in xrange(length):
    x = n
    y = n + 1
    n = n + 1

    old_second_numerator = second_numerator
    old_second_denominator = second_denominator

    second_numerator = x * first_numerator + y * second_numerator
    second_denominator = x * first_denominator + y * second_denominator

    first_numerator = old_second_numerator
    first_denominator = old_second_denominator

    a = first_numerator / first_denominator
    b = second_numerator / second_denominator

    while a == b:
        result.append(a)
        first_numerator = 10 * (first_numerator % first_denominator)
        second_numerator = 10 * (second_numerator % second_denominator)
        a = first_numerator / first_denominator
        b = second_numerator / second_denominator

print "%i.%s" % (result.pop(0), "".join(map(str, result)))