"""
Ex 6.9 from A Primer on...
We already have a function for computing the
area for a list of coordinates. The only change needed
is that we must look up in a dictionary with keys 1,2,3
rather than a list with indices 0,1,2.
"""

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

corners = {1:(0,0),2:(1,0),3:(0,2)}

answer = f"""The area of a triangle with corners {corners[1]}, {corners[2]},
and {corners[3]} is {triangle_area(corners)}."""

print(answer)

"""
Terminal> python area_triangle_dict.py 
The area of a triangle with corners (0, 0), (1, 0),
and (0, 2) is 1.0.
"""