TypeError: list indices must be integers, not float

It looks like you are using Python 3.x. One of the important differences in Python 3.x is the way division is handled. When you do x / y, an integer is returned in Python 2.x because the decimal is truncated (floor division). However in 3.x, the / operator performs 'true' division, resulting in a float instead of an integer (e.g. 1 / 2 = 0.5). What this means is that your are now trying to use a float to reference a position in a list (e.g. my_list[0.5] or even my_list[1.0]), which will not work as Python is expecting an integer. Therefore you may first want to try using middle = (first + last) // 2, adjusting so that the result returns what you expect. The // indicates floor division in Python 3.x.

Kinda late to the party but you could also use:

middle = int((first + last) / 2)

In any case why you are getting your error is perfectly explained in RocketDonkey answer.

For your code to work you should also set:

position = binary_search(names, entered)

as Hugo Ferreira mentioned.

Also check this question: What is the difference between '/' and '//' when used for division?

I had this problem when using ANN and PyBrain on function testOnData().

So, I solved this problem putting "//" instead "/" inside the index on backprop.py source code.

I changed:

print(('Max error:',     max(ponderatedErrors),     'Median error:',     sorted(ponderatedErrors)[len(errors) / 2])) # <-- Error area 

To:

print(('Max error:',     max(ponderatedErrors),     'Median error:',     sorted(ponderatedErrors)[len(errors) // 2])) # <-- SOLVED. Truncated

I hope it will help you.