没有附加到列表的项目,或者在python中返回为空的列表？

Question

在我的代码中,项目percentgrade不会在for循环的每次迭代中附加到列表lnpercentgrade,但我不确定原因.当我尝试在lnpercentgrade中汇总项目时(在代码的末尾),我返回0因为lnpercentgrade是empy.我将lnpercentgrades声明为maininput()函数之外的全局变量,因为当我尝试求和(lnpercentgrades)时,在代码的底部,我返回"lnpercentgrades not defined".

我猜想lnpercentgrades在maininput()函数内部没有被修改,即使我确信我在.append函数之前正确输入了它.

我真正想要做的是将总和(lnpercentgrades)与100匹配,但是当我输入5项全部值为20时,总和为0而不是100.

重要的线条标有箭头<<<<<<<<<<<<<<<<<<<<<

lnpercentgrades = []   <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
def maininput():
    numtests = int(input("Enter # of tests:"))
    numassign = int(input("Enter # of assignments:"))
    numquizzes = int(input("Enter # of quizzes:"))
    numlabs = int(input("Enter # of labs:"))

    l = [numtests, numassign, numquizzes, numlabs]
    ln = ["test", "assignments", "quizzes", "labs"]
    lnpercentgrades = [] <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    testwavg = None
    numassignwavg = None
    numquizzeswavg = None
    numlabswavg = None
    numfinalwavg = None

    lnwavg = [testwavg, numassignwavg, numquizzeswavg, numlabswavg]
    print(l[0])
    print("Is there a separately weighted final?")
    yn = int(input("Enter 1 for yes. 2 for no:"))
    while (yn > 2 or yn < 1):
        yn = int(input("Enter 1 for yes. 2 for no, please:"))

    n = 4 
    if yn == 1:
        final = 1
        l.append(final)
        ln.append("final")
        lnwavg.append(numfinalwavg)
        n = 5


    for i in range (n):
        if l[i] > 0:
            print("Enter % of total grade of",ln[i],":") 
            percentgrade = float(input("")) 
            print("you inputed:", percentgrade)
            lnpercentgrades.append(percentgrade) <<<<<<<<<<<<<<<<<<<<<<
            percentgrade = percentgrade*.01 


            varscoreslist = []
            for x in range(l[i]):
                print("Enter score of", ln[i], x+1,"as a fraction:")
                from fractions import Fraction
                inputfrac = input("")
                varscore = float(sum(Fraction(s) for s in inputfrac.split())) 
                #the above converts fractional inputs to decimals
                varscoreslist.append(varscore)

            if ln[i] == "labs":
                score = sum(varscoreslist)
            else:
                sumscores = sum(varscoreslist)
                score = sumscores/l[i]

            lnwavg[i] = score*percentgrade

maininput()
print(lnpercentgrades)
print("sum of percent of grades", sum(lnpercentgrades)) <<<<<<<<<<<<<<<

if float(sum(lnpercentgrades)) != 100:  <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    print("Sorry, the grade percent of each item enter did not sum to 100:")
    print("Program will rerun.")
    input("")
    maininput()

coursegrade = sum(lnwavg)
print("Your course grade is:", coursegrade)

input("")

Answer 1

乍一看,看起来你可能有一个范围问题.您正在修改函数内部的列表,但请记住,这是列表的本地副本.尽管您在外部范围内声明它,但您没有使用它global,这意味着它会创建一个函数本地副本,执行其业务然后退出,而不会影响"主"列表.

我建议修改你的函数以返回你想要的列表,这样你就可以按照你的期望使用它们.这是一个基本的例子:

def MyFunc():
    l1 = ['my', 'first', 'list']
    l2 = ['another', 'list']
    return l1, l2

main_list, second_list = MyFunc()

print(main_list)
print(second_list)

哪个会输出:

['my', 'first', 'list']
['another', 'list']

如果你真的想要将变量保留在外部作用域中,你必须global在函数内部开头(我可能会使用第一种方法):

main_list = []
second_list = []

def MyFunc():
    global main_list
    global second_list
    main_list = ['more', 'good', 'stuff']
    second_list = ['another', 'list']


MyFunc()

print(main_list) # ['more', 'good', 'stuff']
print(second_list) # ['another', 'list']