Add two points on a elliptic curve

ECadd.py

# Predfined parameters (x1,y1,x2,y2 are integers)
A = (x1,y1); B = (x2,y2)

# Function
def ECadd(A,B):
    lambda_mod = (B[1]-A[1])% P * modular_inverse(B[0]-A[0], P)
    x3 = (lambda_mod * lambda_mod - A[0] - B[0]) % P
    y3 = (lambda_mod * (A[0] - x3) - A[1]) % P
    return (x3,y3)