Calculate GCD between 2 numbers and shows the working behind it

gcd.py

import sys

if len(sys.argv) < 3:
    print("Usage: python test.py A B")
    sys.exit(1)

A,B = int(sys.argv[1]), int(sys.argv[2])

if B < 0:
    print("B should be positive.")
    sys.exit(1)

if A < B:
    if A < 0:
        A, B = B, A
else:
    A, B = B, A


backsub = []
r = 0
r_dict = {
    "({})".format(A): "a",
    "({})".format(B): "b"
}

def egcd(a, b):
    global r
    if a == 0:
        return (b, 0, 1)
    else:
        r += 1
        r_dict["({})".format(b%a)] = "r{}".format(r)
        print("{} = {} x {} + {}  --- r{} = {}".format(b, a,b//a, b%a, r, b%a))
        output =  "({}) = ({}) - {} x ({})  \n".format(b%a,b,b//a,a)
        output += "   = {} - {} x {}\n".format(b,b//a,a)

        gcd, x, y = egcd(b % a, a)
        output += "   = {}\n".format(b%a)

        backsub.append(output)

        return (gcd, y - (b//a) * x, x)

print("="*30,"GCD Working","="*30)
gcd, x, y = egcd(A,B)

print("="*30,"Remainder Working","="*30)

for line in backsub[:0:-1]:
    for sub in r_dict:
        line = line.replace(sub, r_dict[sub])
    print(line)

print("="*30,"Results","="*30)
print("gcd = {}".format(gcd))
print("    = ({})({}) + ({})({})".format(A,x,B,y))