Ackermann Expander

print("Ackermann function expander")
print("Ackermann function: ")
print("""ack(m, n):
    ans = 0
    if m == 0:
        ans = n + 1
    elif n == 0:
        ans = ack(m - 1, 1)
    else:
        ans = ack(m - 1, ack(m, n - 1))
    return ans
""")
def ack(m,n):
    ans = 0
    if m == 0:
        ans = n + 1
    elif n == 0:
        ans = ack(m - 1, 1)
    else:
        ans = ack(m - 1, ack(m, n - 1))
    return ans
    # This isn't actually used, all the ackering is done in the one below
def ackEx(ackFunctionString):
    inp = ackFunctionString[4:-1]
    inp = inp.split(",")
    m = int(inp[0])
    n = int(inp[1])
    ans = ""
    if m == 0:
        ans = str(n + 1)
    elif n == 0:
        ans = "ack(" + str(m - 1) + ", " + "1)"
    else:
        ans = "ack(" + str(m - 1) + ", ack(" + str(m) + ", " + str(n -1) + "))"
    return ans

def FindLowestFunction(s, func):
    #(String with expression, function prefix (ie, in sin(2 + sin(3 - sin(4 + x))), use FLF(..., sin)
    Open = "("
    Close = ")"
    startIndex = 0
    endIndex = 0
    index = 0
    for char in s:
        if char == Open:
            startIndex = index
        elif char == Close:
            endIndex = index
            break
        index += 1
    startIndex -= len(func)
    res = [s[:startIndex], s[startIndex:endIndex + 1], s[endIndex + 1:]]
    return res


inp = input("Type 2 integers, seperated by a comma: ")
print("Press enter to expand the next line.")
func = ""
while inp:
    try:
        inp = inp.split(",")
        m = int(inp[0])
        n = int(inp[1])
        done = False
        func = "ack({0}, {1})".format(m, n)
        print(" = " + func)
        func = ackEx(func)
        while not done:
            func = FindLowestFunction(func, "ack")
            func = func[0] + ackEx(func[1]) + func[2]
            print(" = " + func, end = "")
            if func[0] != "a":
                done = True
                print("\nDone!")
            input()
    except ValueError:
        print("There was a ValueError. Make sure the input is formatted correctly.")
    except IndexError:
        print("There was an IndexError. Make sure you type in two numbers.")
    inp = input("Type 2 integers, seperated by a comma:")
    print("Press enter to expand the next line.")