如何在python中的一个块中写多个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。

最好的祝福

Answer 1

如果你真的不关心异常，你可以循环遍历案例直到你成功：

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

这至少避免了每个案例都必须缩进一次。 如果不同的函数需要不同的参数，你可以使用functools.partial在循环之前“填充”它们。

Answer 2

我会为此写一个快速包装函数first() 。

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

这似乎是一件非常奇怪的事情，但我可能会在没有异常的情况下循环使用函数并突破：

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

Answer 4

您应该指定每次尝试捕获的异常类型。

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

等等。

Answer 5

这是我发现的最简单的方法，只是将尝试嵌入前面的除外。

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

Answer 6

如果你想要多个 try 语句，你可以这样做，包括 except 语句。 提取（重构）您的陈述。 并使用 and 和 or 的魔力来决定何时短路。

python def a(): try: # a code except: pass # or raise else: return True

def b():
    try: # b code
    except: pass # or raise
    else: return True

def c():
    try: # c code
    except: pass # or raise
    else: return True

def d():
    try: # d code
    except: pass # or raise
    else: return True

def main():   
    try:
        a() and b() or c() or d()
    except:
        pass

Answer 7

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