typeerror, building histogram from data

[newatpython11]

I am trying to run a code to build histogram from a list of data and keep getting the below error :

Error:
TypeError: list indices must be integers or slices, not float

Below is my code, can you help me with what i am doing wrong?

%matplotlib inline
import numpy as np
import matplotlib.pyplot as plt
from helper import plotHisto

data = np.loadtxt('math_scores.txt')
def myMap(inp, f) :
    res = []
    for i in inp :
        res.append(f(i))
    return res

def new(x) : return int(x)
pdata = myMap(data, new)

def buildHisto(pdata, numbins, minimum, maximum) :

    minimum = min(pdata)
    maximum = max(pdata)
    diff = maximum - minimum
    binwidth = diff/numbins
    histo = []
    for d in pdata :
        histo[d//binwidth]+=1
    return histo

histo = buildHisto(pdata, 10, minimum, maximum)
plotHisto(histo, 'histo1.png', minimum, maximum, plotinline = True)