Question

我将提供该代码应该执行的任务的描述，以防万一有人需要它来回答我。

#Write a function called "load_file" that accepts one 
#parameter: a filename. The function should open the
#file and return the contents.#
#
# - If the contents of the file can be interpreted as
#   an integer, return the contents as an integer.
# - Otherwise, if the contents of the file can be
#   interpreted as a float, return the contents as a
#   float.
# - Otherwise, return the contents of the file as a
#   string.
#
#You may assume that the file has only one line.
#
#Hints:
#
# - Don't forget to close the file when you're done!
# - Remember, anything you read from a file is
#   initially interpreted as a string.


#Write your function here!
def load_file(filename):
    file=open(filename, "r")
    try:
        return int(file.readline())
    except ValueError:
        return float(file.readline())
    except:
        return str(file.readline())
    finally:
        file.close()


#Below are some lines of code that will test your function.
#You can change the value of the variable(s) to test your
#function with different inputs.
#
#If your function works correctly, this will originally
#print 123, followed by <class 'int'>.
contents = load_file("LoadFromFileInput.txt")
print(contents)
print(type(contents))

使用包含“ 123”的文件测试代码时，一切正常。当网站加载另一个文件以测试此代码时，会发生以下错误：

[Executed at: Sat Feb 2 7:02:54 PST 2019]

    We found a few things wrong with your code. The first one is shown below, and the rest can be found in full_results.txt in the dropdown in the top left:

    We tested your code with filename = "AutomatedTest-uwixoW.txt". We expected load_file to return the float -97.88285. However, it instead encountered the following error:

    ValueError: could not convert string to float:

因此，我猜测该错误发生在第一个except语句内，但我不明白为什么。如果将文件中的值转换为float时发生错误，代码是否应该转到第二个except语句？然后在第二个except中将其转换为字符串，该字符串仍然可以工作吗？我猜我对try-except(specified error)-except(no specified error)的工作方式有误解。

对不起，很长的帖子。

Answer 1

该代码是否应转到除语句之外的第二个语句？

都能跟得上：这个 “平坦” 的try / except语句仅适用于在第一 try块。如果在那里发生异常，则except分支将捕获此异常并立即评估适当的块。如果在该块中发生了异常，它不被任何东西卡住，因为没有try块在那里。

因此，您必须做很多嵌套的try / except语句：

try:
    do_this()
except ValueError:
    try:
        do_that()
    except ValueError:
        do_this()
    except:
        do_that_one()
except:
    # a whole bunch of try/except here as well

您可能需要添加更多级别的嵌套。

就需要编写的代码量而言，这是非常低效的。更好的选择可能是：

data = file.readline()
for converter in (int, float, str):
    try:
        return converter(data)
    except:
        pass

请注意，如果你做converter(file.readline())，新的生产线将在每次迭代（/或，你的情况，在任何新的尝试，除了块）读取，这可能不是你所需要的。

Answer 2

否，将仅执行那些except块中的一个-第一个与异常匹配的块。您描述的行为将与

相对应

except ValueError:
    try:
        return float(file.readline())
    except:
        return str(file.readline())

Answer 3

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Python try-except-except

3 个答案: