"""Ex. 6.9 from 'A primer on...' 
Minor modification of the code from ex 3.16. The function
should perform the same calculations, but the argument is
a dictionary instead of a list"
"""


def triangle_area(v):
    [x1,y1] = v[1]
    [x2,y2] = v[2] 
    [x3,y3] = v[3]  
    A = abs(0.5*( (x2*y3)-(x3*y2)-(x1*y3)+(x3*y1)+(x1*y2)-(x2*y1) ))
    return A

v1 = (0,0);  v2 = (1,0);  v3 = (0,2)
#vertices = [v1, v2, v3]
vertices = {1:v1,2:v2,3:v3}

print(triangle_area(vertices))


"""
Terminal> python area_triangle_dict.py 
1.0
"""