为什么每个字母的等级都一样？

Question

我的任务是创建一个程序，打开并读取文本文件，计算成绩（包括平均权重），给出最终成绩，将其更改为字母成绩，然后将其写入新的文本文件。在分数转换成字母分数之前，一切都很顺利。所有的分数都在70-89之间，所以我没有费心为A、B或E（F）设置任何其他代码。每当我试图把成绩转换成字母成绩时，每个人的成绩都会变成C。我哪里出错了？你知道吗

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

if printedgrade >= 70 <= 79:

应该是

if printedgrade >= 70 and printedgrade <= 79:

你也可以这样做：

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

Answer 2

因为你的if总是在计算true，因为它是无序的。应该是：

70 <= printedgrade <= 79

你的陈述总是正确的，因为正如你所说的，所有的分数都是70-89，所以printedgrade将大于或等于70，而70小于79，所以它总是True。你知道吗

尽管我强烈建议让你的代码适用于所有年级。你不能假设，因为这一次成绩总是在一定范围内。你知道吗