Python - TypeError: 'float' object has no attribute 'getitem'

Question

I ran the following code in Python 2.7 and got an error. Why?

CODE:

def triangle_area(a, b, c):
    """
    Returns the area of a triangle given the length of three sides
    Code source: [here][1]
    """
    def distance(p1, p2):
        return math.hypot(p1[0]-p2[0], p1[1]-p2[1])

    side_a = distance(a, b)
    side_b = distance(b, c)
    side_c = distance(c, a)
    s = 0.5 * ( side_a + side_b + side_c)
    return math.sqrt(s * (s - side_a) * (s - side_b) * (s - side_c))

Running the following: y = triangle_area(10.1,1.1,11.2)

Produces this error: Traceback (most recent call last):

[snip]
....in distance
return math.hypot(p1[0]-p2[0], p1[1]-p2[1])
TypeError: 'float' object has no attribute '__getitem__'

You're sending floating-point numbers to the distance function, which then tries to index them. You can't do that. What are you expecting it to do? — TigerhawkT3
– TigerhawkT3, Commented Aug 27, 2015 at 21:10
I think you have nailed it. I found this code at code.activestate.com/recipes/576896-3-point-area-finder and, wrongly, assumed it worked. Off to recode... — WyomingGeezer
– WyomingGeezer, Commented Aug 27, 2015 at 21:13
Agreed! I think the found code was intended to pass three points (x,y) rather than the scalars I am sending. I'll work up the solution and post it as an answer. Your comments helped me discover the problem. TNX — WyomingGeezer
– WyomingGeezer, Commented Aug 27, 2015 at 21:22

Chad S. · Accepted Answer · 2015-08-27 21:37:54Z

1

The distance function in this snippet is assuming that you will pass it tuples for the (x,y) position of the points.

So to compute the area of a triangle with vertices at (0,0), (0,1), (1,1) you would call

triangle_area((0,0), (0,1), (1,1))

answered Aug 27, 2015 at 21:37

Chad S.

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1 Comment

WyomingGeezer Over a year ago

Yup! I discovered that I was thinking the function handled the length of sides. WRONG! It, as you noted, handles the position of three points. TNX for your answer.

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