Calculate area and perimeter of any triangle

#!/usr/bin/python3
import sys, math
a, b, c = map(float, sys.argv[1:])
if a + b <= c or a + c <= b or b + c <= a:
    print("Error: not a valid triangle")
    sys.exit(1)
peri = a + b + c
area = math.sqrt((a + b + c) *
                 (a + b - c) *
                 (a - b + c) *
                 (-a + b + c)) / 4
print("Perimeter =", peri)
print("Area =", area)