try-except 块：如果引发异常，则类似于“else”

Question

I have this kind of code:

try:
    return make_success_result()
except FirstException:
    handle_first_exception()
    return make_error_result()
except SecondException:
    handle_second_exception()
    return make_error_result()

And I'm wondering is there any way I can achieve this:

try:
    # do something
except Error1:
    # do Error1 specific handling
except Error2:
    # do Error2 specific handling
else:
    # do this if there was no exception
????:
    # ALSO do this if there was ANY of the listed exceptions (e.g. some common error handling)

So the code is executed in one of following sequences:

try > else > finally
try > except > ???? > finally

EDIT: my point here is that ???? block should execute right after ANY of the except blocks, meaning that it's an addition to error handling, not a substitution.

Answer 1

What I would do in that case is to set a boolean when you get an exception, like so:

got_exception = False
try:
    # do something
except Error1:
    # do Error1 specific handling
    got_exception = True
except Error2:
    # do Error2 specific handling
    got_exception = True
else:
    # If there was no exception
finally:
    if got_exception:
        # ALSO do this if there was ANY exception (e.g. some common error handling)

This should fit your needs, which is IMO the cleanest way of combining all of the solutions which have been presented into the most readable code structure that's going to be the easiest to debug.

Answer 2

You can do:

try:
    # Do something
except Error1:
    # Do Error1 specific handling
except Error2:
    # Do Error2 specific handling
except Exception:
    # Handle any other exception (Generic exception handling)
else:
    # Do this if there were no exceptions
finally:
    # Execute this regardless

Answer 3

You can actually do this:

try:
    print 'try'
    # 1/0
    # {}[1]
    # {}.a
except AttributeError, KeyError:  # only handle these exceptions..
    try:
        raise                     # re-raise the exception so we can add a finally-clause executing iff there was an exception.
    except AttributeError:
        print 'attrerr'
        # raise ...               # any raises here will also execute 'common'
    except KeyError:
        print 'keyerror'
    finally:                      # update 0: you wanted the common code after the exceptions..
        print "common"

else:
    print 'no exception'

but it is horrid and I would not suggest that you do without copious amounts of comments describing why..

UPDATE: you don't need to catch anything but the interesting exceptions in the inner try-block. Code updated.

UPDATE2: per OP's clarification, common should just be executed when an interesting exception is thrown. Code updated. @MattTaylor's version is definitely the way to go ;-)

Answer 4

Yes, exception handling in python includes both an else and a finally clause. You can do this:

try:
    # do something
except Error1:
    # do Error1 specific handling
except Error2:
    # do Error2 specific handling
else:
    # do this if there was no exception
finally:
    # Do this in any case!

The python docs mention these blocks, even though it doesn't show the full example you need.

---

EDIT: I see that you do not ask specifically for the clean-up in the general case. Python docs put it this way:

The try statement has another optional clause which is intended to define clean-up actions that must be executed under all circumstances.

Note that the finally will run whether there was an exception or not. Combined with the else block, you should still be able to do what you want.

Answer 5

You could trap all errors and check for its type in the error handling code like this:

try:
    # do something
except Exception as e:
    if isinstance(e, Error1):
        # do Error1 specific handling
    elif isinstance(e, Error2):
        # do Error2 specific handling
    else:
        # do non-Error1/Error2 handling
    # ALSO do this if there was ANY exception (e.g. some common error handling)
else:
    # do this if there was no exception