为什么这打印相同的字母等级？

Question

我的赋值是创建一个程序从文本文件打开和读取，计算等级，包括普通权重，给出最终成绩，将其更改为字母等级，然后将其写入新的文本文件。一切都在努力，直到将点转换为字母等级。所有等级都在70-89之间，因此我还没有打扰任何其他代码为A，B或E（f）。每当我尝试将成绩转换为字母等级时，它会将每个人的成绩改为C.我出错了吗？

infile = open("c:\\Python34\\MyFiles\\ClassGradebook.txt","r")  
outfile = open("c:\\Python34\\myfiles\\ClassGrades.txt","w") 

aline = infile.readline()  # uses readline method to read the first line of the file

def quizsum():
        quizsum1 = quiz1 + quiz2 + quiz3
        quizavg = (quizsum1 / 30) * .3
        return float(quizavg)

def midtermsum():
        midtermsum1 = midterm1 + midterm2
        midtermavg = (midtermsum1 / 200) * .4
        return float(midtermavg)

def finalsum():
        finalsum1 = final1
        finalavg = (finalsum1 / 100) * .3
        return float(finalavg)
def lettergrade():
        if printedgrade >= 70 <= 79:
                return "C"
        else:
                return "B"       

while aline:
        items = aline.split()   
        dataline = items[0] + " " + items[1] 
        quiz1 = int(items[2])
        quiz2 = int(items[3])
        quiz3 = int(items[4])
        midterm1 = int(items[5])
        midterm2 = int(items[6])
        final1 = int(items[7])
        quizavg = quizsum()
        midtermavg = midtermsum()
        finalavg = finalsum()
        gradetotal = quizavg + midtermavg + finalavg
        printedgrade = gradetotal * 100
        printedgrade2 = lettergrade()
        print(dataline)
        print(printedgrade2)
        outfile.write(printedgrade2 + '\n')   newline character
        aline = infile.readline()   

infile.close()  
outfile.close()  

.

Answer 1

因为您的if始终是真实的，因为它是无序的。它应该是：

70 <= printedgrade <= 79

您的语句始终评估为真，因为当您所说，所有等级都是70-89，因此printedgrade将大于或等于70，70小于79，因此它将始终是生成的。

虽然我强烈建议使您的代码适用于所有等级。你不能假设，因为这次等级在一定的范围内，它们总是会。

Answer 2

if printedgrade >= 70 <= 79:

.

应该是

if printedgrade >= 70 and printedgrade <= 79:

.

你也可以做一些这样的事情：

if printedgrade >= 90:
    return "A"
elif printedgrade >= 80:
    return "B"
elif printedgrade >= 70:
    return "C"
...

.