Question

我有这段代码，无论出于何种原因，它会在执行后返回none。有谁知道为什么？

def function():
    try:
        ctr = 0
        total = 0
        file = open("text.txt", 'r')
        while ctr <= 15:
            ctr += 1
            for line in file:
                line = line.strip("\n")
                num = float(line)
                total += num
        average = total / 15
        return average
    except ValueError:
        total = total

Answer 1

在值错误之后，您没有返回任何内容。

   except ValueError:
        total = total 
        return ???

你确定float（line）不是导致可能的ValueError的错误的来源吗？

Answer 2

放入评论太多了，但这段代码的输出是什么？

def function():
    average = 0

    try:
        ctr = 0
        total = 0
        file = open("text.txt", 'r')
        while ctr <= 15:
            ctr += 1
            for line in file:
                line = line.strip("\n")
                num = float(line)
                total += num
        average = total / 15
        return average
    except ValueError as e:
        total = total #What?
        print("Caught ValueError")
        return e
    except Exception as e:
        print("Caught Exception")
        return e
    print("At the end...")
    return False

ve = function()

Answer 3

如果我了解您要执行的操作，则需要读取文件并计算其中包含的数字的平均值，而忽略包含非数字的任何行。您当前的代码无法正确执行此操作，因为try和except的级别太高。你也有两个循环，你可能只需要一个。

尝试在文件内容的单个循环内移动异常处理：

def function():
    ctr = 0
    total = 0

    with open("text.txt", 'r') as file:   # a with statement will close the file for you
        for line in file:   # just one loop
            try:
                num = float(line)   # this may raise an exception!
                ctr += 1
                total += num
            except ValueError:   # ignore ValueError exceptions in the loop
                pass

    if ctr > 0:
        average = total / ctr
    else:
        average = 0   # or maybe raise an exception here, for a file with no numbers?

    return average

如果您需要将平均值限制为15个值，则可以在循环中添加ctr大于15的额外检查。我把那部分遗漏了，因为从你的非工作代码中你不清楚你想要做什么（计算行数或计数？）。

功能没有返回，我不知道为什么

3 个答案: