Python passed values from a list not adding correctly -

in code below having issues 2 things. 1 math in function on lines 40 (exampoints) , 47 (hwkpoints) being passed range of values in list on line 94. should taking scores , adding them reason isn't adding last number on each range passed.

ex: myvalues[11:13] being passed numbers 75, 95, , 97 adds first 2 , not last.

my code here:

from time import asctime time import localtime  def findgrade(mygrade): #argument number in range of 1 - 100 or float mynum?     if mygrade >= 90:         lettergrade = "a"     if mygrade >= 80:         lettergrade = "b"     if mygrade >= 70:         lettergrade = "c"     if mygrade >= 60:         lettergrade = "d"     if mygrade < 60:         lettergrade = "f"     return lettergrade  def calculatepointsearned(hwkgrades, examgrades):     hwktotal = float(hwkpoints(hwkgrades))     #print hwktotal     examtotal = float(exampoints(examgrades))     #print examtotal     myaverage = (hwktotal + examtotal) / possiblepoints     myaverage = myaverage * 100.0     #myaverage = int(myaverage)     return myaverage  def totalpoints(hwkgrades, examgrades):     hwktotal = int(hwkpoints(hwkgrades))     examtotal = int(exampoints(examgrades))     allpoints = str((hwktotal + examtotal))     return allpoints   #create newtimeline using day of week, space, month, space, day, space, year, space time asctime function def timemessage():     localtime()     newtimeline = asctime()     return newtimeline  def exampoints(examvalues):     mygrades = 0     grade in examvalues:         mygrades = int(grade) + mygrades     #print str(mygrades) + " exam\n"      return mygrades  def hwkpoints(hwkvalues):     mygrades = 0     grade in hwkvalues:         mygrades = int(grade) + mygrades     #print str(mygrades) + " hwk"      return mygrades  def requestmessage (myvalues, mytime):     nameline = myvalues[1] + ", " + myvalues[2] + "\t" + myvalues[0] + "\t" + myvalues[3]     examscore = "exam " + "- " + myvalues[11] + ", " + myvalues[12] + ", " + myvalues[13]     hwkscore = "homework " + "- " + myvalues[4] + ", " + myvalues[5] + ", " + myvalues[6] + ", " + myvalues[7] + ", " + myvalues[8]  + ", " + myvalues[9] + ", " + myvalues[10]     pointsearned = "total points earned " + "- " + totalpoints(myvalues[4:10], myvalues[11:13])     mygrade = "grade:  " + str(theaverage) + " " + findgrade(theaverage)     message = nameline + "\n" + examscore + "\n" + hwkscore + "\n" + pointsearned + "\n" + mygrade + "\n" + mytime     return message  def fileoutput(studentid, lastname, firstname, datetime):     myline = studentid + " " + lastname + ", " + firstname + " " + datetime + "\n"     return myline   #create input stream grades.dat , assign infile infile = open('grades.dat', "r")  #create output stream results.dat , assign outfile outfile = open('results.dat', 'w+')  mytime = timemessage() theaverage = 0 thelettergrade = "" themessage = "" possiblepoints = 550 therequest = ""  studentid = raw_input("please input student id: ") myline = "notemptystring"  while myline != "": #may wrong myline not equal empty string?     myline = infile.readline() #may wrong read line infile , assign myline     myline = myline.strip('\r\n')      myvalues = myline.split(",") #separate values in myline , assign myvalues      if studentid == myvalues[0]:         #print myvalues          #call calculatepointsearned function list of homework values , list of exam values , assign theaverage         theaverage = calculatepointsearned(myvalues[4:10], myvalues[11:13])         #print theaverage          thelettergrade = findgrade(theaverage) #call findgrade function theaverage , assign thelettergrade)         #print thelettergrade          #call fileoutput function studentid, lastname, firstname, , datetime message writing output file, , assign therequest         therequest = fileoutput(myvalues[0], myvalues[1], myvalues[2], timemessage())         #print therequest          themessage = requestmessage(myvalues, timemessage()) #call requestmessage myline , mytime message display, , assign themessage          #write therequest outfile         outfile.write(therequest)          print themessage      else: #is studentid not equal first element in myvalues         "do nothing"   #close infile , outfile infile.close() outfile.close() 

edit: sorry link having problems getting code right on here.

for myvalues[11:13] being passed numbers 75, 95, , 97 adds first 2 , not last

myvalues[11:13] selects 2 elements, not three. end index (13) not included in range.

have read of explain python's slice notation