GPA Calculator with .csv File

"""This is static program
    if you want to use with other csv file,
    you need to change some variable"""
 
import csv  #import to enable read csv file

semester_range = [[3,10],[15,22],[27,33],[38,41],[46,50],[55,59],[64,66]]   #range of subject that contain in each semester
count_row = 0                   
count_semester = 0          
subject = list()            #correct info of each subject Ex. Unit, grade

GPA=0                       #GPA=(Sum_unitxgrade)%Sum_Unit
unit_sum = 0
unitxgrade_sum = 0

with open('GPA.csv',encoding="utf8") as csvfile:            #open file
    spamreader = csv.reader(csvfile)                        #set opened file as variable name spamreader
    for row in spamreader:                                  #read the file in each row
        count_row=count_row+1                               #count row
        if (count_semester<=len(semester_range)-1):                 #check semester
            if (count_row>=semester_range[count_semester][0] and count_row<=semester_range[count_semester][1]):     #row is in semester range
                subject.append([row[1],row[2]])                     #correct in subject list
                if (count_row==semester_range[count_semester][1]):  #if this isn't last semester
                    count_semester=count_semester+1                 #then count semester +1

for i in range(len(subject)):                                           #loop for calculate GPA
    subject[i].append(float(subject[i][0])*float(subject[i][1]))        #calculate unit*grade for 
    unit_sum = unit_sum + float(subject[i][0])                          #calculate sum of unit
    unitxgrade_sum = unitxgrade_sum + float(subject[i][2])              #calculate sum of unit*grade
    
GPA=unitxgrade_sum/unit_sum             #calculate GPA

print ("GPA = "+str(GPA))

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