How to write multiple try statements in one block in python?

问题

I want to do:

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

If do() fails, execute do2(), if do2() fails too, exceute do3() and so on.

best Regards

回答1:

I'd write a quick wrapper function first() for this.

usage: 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'

回答2:

If you really don't care about the exceptions, you could loop over cases until you succeed:

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

This at least avoids having to indent once for every case. If the different functions need different arguments you can use functools.partial to 'prime' them before the loop.

回答3:

It seems like a really odd thing to want to do, but I would probably loop over the functions and break out when there were no exception raised:

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

回答4:

You should specify the type of the exception you are trying to catch each time.

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

and so on.

回答5:

Here is the simplest way I found, just embed the try under the previous except.

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

回答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

来源：https://stackoverflow.com/questions/13874666/how-to-write-multiple-try-statements-in-one-block-in-python

标签

python

exception

exception-handling