Coordinate arithmetic experimentation

x_range = 20
y_range = 20

def pow(a, b):
    if b == 0: return 1
    elif b == 1: return a
    elif b%2 == 1: return a*pow(a, b-1)
    else:
        c = pow(a, b/2)
        return c*c

def tet(a, b):
    if a <= 0: return 0
    elif a == 1: return b
    else: return tet(a-1, pow(b, b))

def t(n):
    divs = 1
    for d in range(2, n+1):
        if n%d == 0: divs += 1
    return divs

def s(n):
    divs = 1
    for d in range(2, n+1):
        if n%d == 0: divs += d
    return divs

def graph():
    # x_range = int(raw_input("Enter range for x: "))
    # y_range = int(raw_input("Enter range for y: "))
    condition = raw_input("Enter a condition: ")

    with file('out.txt', 'w') as output:
        for y in range(1, y_range+1):
            line = ""
            for x in range(1, x_range+1):
                if (eval(condition)): line += 'x '
                else: line += '  '
            print line
            output.write(line+"\n")

while (True):
    try: graph()
    except: break