typeerror, building histogram from data

[newatpython11]

So i tried that and also moved diff out, but now it goes back to the original error i got. Now i have already converted the list to integer, since the original list is made of 50000 datapoints which have data with decimals. not sure what's going on!

%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) :   
    histo = []
    binwidth = diff/numbins
    for d in pdata :
        histo[d//binwidth]+=1
    return histo

minimum = min(pdata)
maximum = max(pdata)
diff = maximum - minimum

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

Error:
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-36-a1b9b926837f> in <module>()
     26 
     27 
---> 28 histo = buildHisto(pdata, 10, minimum, maximum)
     29 plotHisto(histo, 'histo1.png', minimum, maximum, plotinline = True)

<ipython-input-36-a1b9b926837f> in buildHisto(pdata, numbins, minimum, maximum)
     18     binwidth = diff/numbins
     19     for d in pdata :
---> 20         histo[d//binwidth]+=1
     21     return histo
     22 

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