用Python对列表求和

Question

我已经从CSV文件中导入了值，该文件在第1列中有日期，在第2列中有美元值。我打开它，计算了每行每月的变化。这些更改mthchangeprofit已附加到列表monthlychange中

我想用monthlychange的和除以count（6）来计算平均月变化。我已将monthlychange转换为名为sum_mthly的float。平均变化应计算为-450美元/6=-75美元。数据文件中不存在C列和D列。为了便于比较，我将它们添加到图像中

两个问题：

1. sum_mthly正在获取上一个月的变化，而不是将整个列表相加

2. 尽管是integer，但如果没有“浮点零除错误”，我不能用countofchanges替换数字6。它打印出“6”

   # Open the CSV.
    with open(file, newline="") as csvfile:
        csvreader = csv.reader(csvfile, delimiter=",")
        csvheader = next(csvreader)
   
    # Initialize variables as zero.
    count = 0
    beginprofit = 0
   
    # Conducting the ask
    for row in csvreader:    
    #Count the number months.
    count = count + 1 
   
    # Create data lists to append data rows to.
    monthlychange = []
   
    #Calculate the monthly change in profits.
    endprofit = int(row[1])
    mthchangeprofit = endprofit - beginprofit
   
    #Store these monthly changes in a list
    monthlychange.append(mthchangeprofit)
   
    beginprofit = endprofit
   
    #Calculate the avg change in profits
    countofchanges = count - 1        #denominator
    sum_mthly = sum(float(mthchangeprofit) for mthchangeprofit in monthlychange)  #numerator
   
    avgchange_profits = sum_mthly/6  #only using last mthly change
   
    print(type(mthchangeprofit))      #integer
    print(type(monthlychange))        #list
    print(type(sum_mthly))            #float
    print(type(countofchanges))       #integer   
    print("----------------------------------------------------------")
    print("Count of Changes: " + str(countofchanges))        #prints "6"
    print("Average Change: " + "$" + str(int(avgchange_profits)))   #prints "$16"