python - 如何在python的一个块中编写多个try语句？

Question

我想要做：

try:
    do()
except:
    do2()
except:
    do3()
except:
    do4()

如果 do() 失败，则执行 do2()，如果 do2() 也失败，则执行 do3() 等等。

此致

Answer 1

如果您真的不关心异常，则可以循环案例直到成功：

for fn in (do, do2, do3, do4):
    try:
        fn()
        break
    except:
        continue

这至少避免了必须为每个案例缩进一次。如果不同的函数需要不同的参数，您可以使用 functools.partial 在循环之前“准备”它们。

Answer 2

我会first()为此编写一个快速包装函数。

用法：value = first([f1, f2, f3, ..., fn], default='All failed')

#!/usr/bin/env


def first(flist, default=None):

    """ Try each function in `flist` until one does not throw an exception, and
    return the return value of that function. If all functions throw exceptions,
    return `default` 

    Args: 
        flist - list of functions to try
        default - value to return if all functions fail

    Returns:
        return value of first function that does not throw exception, or
        `default` if all throw exceptions.

    TODO: Also accept a list of (f, (exceptions)) tuples, where f is the
    function as above and (exceptions) is a tuple of exceptions that f should
    expect. This allows you to still re-raise unexpected exceptions.
    """

    for f in flist:
        try:
            return f()
        except:
            continue
    else:
        return default

# Testing.

def f():
    raise TypeError

def g():
    raise IndexError

def h():
    return 1


# We skip two exception-throwing functions and return value of the last.
assert first([f, g, h]) == 1

assert first([f, g, f], default='monty') == 'monty'

Answer 3

这似乎是一件很奇怪的事情，但我可能会遍历函数并在没有引发异常时中断：

for func in [do, do2, do3]:
    try:
        func()
    except Exception:
        pass
    else:
        break 

Answer 4

这是我找到的最简单的方法，只需在前面的except下嵌入try即可。

try:
    do()
except:
    try:
        do2()
    except:
        do3()

Answer 5

您应该指定每次尝试捕获的异常的类型。

try:
    do()
except TypeError: #for example first one - TypeError
    do_2()
except KeyError: #for example second one - KeyError
    do_3()

等等。

Answer 6

import sys

try:
    f = open('myfile.txt')
    s = f.readline()
    i = int(s.strip())
except OSError as err:
    print("OS error: {0}".format(err))
except ValueError:
    print("Could not convert data to an integer.")
except:
    print("Unexpected error:", sys.exc_info()[0])
    raise