102.wk1.7

from math import sqrt
"""
This function is based on the Triangle Inequality Theorem, which states
that the sum of two side lengths of a triangle is always greater
than the third side. If this is true for all three combinations of added
side lengths, then the sides will form a triangle.
"""
def Is_a_Triangle(a, b, c):
    result = ( (a+b) > c) and ( (a+c) > b) and ( (b+c) > a)
    return(result)

"""
This function is based on Heron's Formula
https://en.wikipedia.org/wiki/Heron%27s_formula
It uses the numerically stable version. Point 5 in the above link.
This, expressed in terms of the variables used is
Area = Sqrt(w*x*y*z)/4
"""
def Area_of_a_Triangle(a, b, c):
    w = (a + (b+c))
    x = (c - (a-b))
    y = (c + (a-b))
    z = (a + (b-c))
    return(sqrt(w * x * y * z) / 4.0)

print("Calculating the area of a triangle.")
print("Input the length of each side, a,b,c, in consistent units.")
print("This means all sides in cm for example.")
Finished = False
while not Finished:
    a = input("Length of side a (0 to exit) : ")
    Finished  = (int(a) == 0)
    if not Finished:
        a = float(a)
        b = input("Length of side b : ")
        b = float(b)
        c = input("Length of side c : ")
        c = float(c)
        if Is_a_Triangle(a, b, c):
            Area = Area_of_a_Triangle(a, b, c)
            print("Area of the triangle is : %.2f"% (Area))
        else:
            print(str(a) + ", " + str(b)  + ", " + str(c) + " is not triangle")

print("bye")