PEP 380中有一个很好的try-else示例。基本上，它归结为在算法的不同部分做不同的异常处理。

大概是这样的:

try:
    do_init_stuff()
except:
    handle_init_suff_execption()
else:
    try:
        do_middle_stuff()
    except:
        handle_middle_stuff_exception()

这允许您在异常发生的地方编写异常处理代码。

错误和异常#处理异常- docs.python.org

The try ... except statement has an optional else clause, which, when present, must follow all except clauses. It is useful for code that must be executed if the try clause does not raise an exception. For example: for arg in sys.argv[1:]: try: f = open(arg, 'r') except IOError: print 'cannot open', arg else: print arg, 'has', len(f.readlines()), 'lines' f.close() The use of the else clause is better than adding additional code to the try clause because it avoids accidentally catching an exception that wasn’t raised by the code being protected by the try ... except statement.

即使你现在想不出它的用途，你可以打赌它一定会有用处的。下面是一个没有想象力的例子:

其他:

a = [1,2,3]
try:
    something = a[2]
except IndexError:
    print("out of bounds")
else:
    print(something)

没有其他的:

try:
    something = a[2]
except IndexError:
    print("out of bounds")

if "something" in locals():
    print(something)

在这里，如果没有抛出错误，则定义了变量something。您可以在try块之外删除它，但如果定义了变量，则需要进行一些混乱的检测。

我发现它非常有用，当你有清理工作要做，即使有例外:

try:
    data = something_that_can_go_wrong()
except Exception as e: # yes, I know that's a bad way to do it...
    handle_exception(e)
else:
    do_stuff(data)
finally:
    clean_up()

使用else样式和可读性是一个重要原因。将可能导致异常的代码放在处理异常的代码附近通常是个好主意。例如，比较这些:

try:
    from EasyDialogs import AskPassword
    # 20 other lines
    getpass = AskPassword
except ImportError:
    getpass = default_getpass

and

try:
    from EasyDialogs import AskPassword
except ImportError:
    getpass = default_getpass
else:
    # 20 other lines
    getpass = AskPassword

当异常不能提前返回或重新抛出异常时，第二个方法很好。如果可能的话，我会这样写:

try:
    from EasyDialogs import AskPassword
except ImportError:
    getpass = default_getpass
    return False  # or throw Exception('something more descriptive')

# 20 other lines
getpass = AskPassword

注意:答案从最近发布的副本复制在这里，因此所有这些“AskPassword”的东西。

我将添加另一个用例，在处理DB会话时看起来很直接:

    # getting a DB connection 
    conn = db.engine.connect()

    # and binding to a DB session
    session = db.get_session(bind=conn)

    try:
        # we build the query to DB
        q = session.query(MyTable).filter(MyTable.col1 == 'query_val')

        # i.e retrieve one row
        data_set = q.one_or_none()

        # return results
        return [{'col1': data_set.col1, 'col2': data_set.col2, ...}]

    except:
        # here we make sure to rollback the transaction, 
        # handy when we update stuff into DB
        session.rollback()
        raise

    else:
        # when no errors then we can commit DB changes
        session.commit()

    finally:
        # and finally we can close the session
        session.close()