python try...finally...的实现方法

try:
  born() # 出生

  # 正常降临世界
  # do something..

except ValueError:
  # 安排错误
  # do something...

except AttributeError:
  # 特征错误
  # do something...

except TypeError:
  # 种类错误
  # do something...

... # 等等杂七杂八的错误

finally:
  go_die() # 挂掉
  come_to_see_me() # 然后来见我
  reincarnate() # 下一轮，安排！

...

finally:
  try:
    go_die()
  finally:
    try:
      come_to_see_me()
    finally:
      reincarnate()

def type_err():
  raise TypeError('this is a type error.')

def after_type_err():
  raise ValueError('this is a value error.')

try:
  type_err()
except TypeError:
  after_type_err()

Traceback (most recent call last):
 File "<ipython-input-4-189a22d65266>", line 8, in <module>
  type_err()
 File "<ipython-input-4-189a22d65266>", line 2, in type_err
  raise TypeError('this is a type error.')
TypeError: this is a type error.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
 File "C:\Users\lineu\AppData\Local\Programs\Python\Python37\lib\site-packages\IPython\core\interactiveshell.py", line 3326, in run_code
  exec(code_obj, self.user_global_ns, self.user_ns)
 File "<ipython-input-4-189a22d65266>", line 10, in <module>
  after_type_err()
 File "<ipython-input-4-189a22d65266>", line 5, in after_type_err
  raise ValueError('this is a value error.')
ValueError: this is a value error.

class FinalExecutor(object):
  """终极执行器
  用于确保你所有的方法都会被执行（不管中途有没有方法报错）
  同时能看到正确的错误信息
  """

  def __init__(self):
    self.last_err = None # 保存最近发生的错误

  def __enter__(self):
    return self

  def __exit__(self, exc_type, exc_val, exc_tb):
    # 如果有发生错误，则抛出
    if self.last_err:
      raise self.last_err

  def call(self, func, *args, **kwargs):
    """调用执行方法"""
    try:
      func(*args, **kwargs)
    except Exception as e:
      # Exception 捕获所有继承自它或它子类的错误类型
      # 捕获它等于捕获几乎所有错误

      if self.last_err:
        # 将本次错误的上下文定义为上一次错误
        e.__context__ = self.last_err

      # 更新为当前错误
      self.last_err = e

# 定义 3 个方法用于测试
def type_err():
  print('type error')
  raise TypeError('x')


def value_err():
  print('value error')
  raise ValueError('x')


def attr_err():
  print('attr error')
  raise AttributeError('x')


# 使用 with 语句来启动终极执行器
with FinalExecutor() as e:
  e.call(type_err)
  e.call(value_err)
  e.call(attr_err)

type error
value error
attr error
Traceback (most recent call last):
 File "<ipython-input-5-1b07c576630b>", line 19, in call
  func(*args, **kwargs)
 File "<ipython-input-6-d602d89ed0e7>", line 3, in type_err
  raise TypeError('x')
TypeError: x

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
 File "<ipython-input-5-1b07c576630b>", line 19, in call
  func(*args, **kwargs)
 File "<ipython-input-6-d602d89ed0e7>", line 8, in value_err
  raise ValueError('x')
ValueError: x

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
 File "C:\Users\lineu\AppData\Local\Programs\Python\Python37\lib\site-packages\IPython\core\interactiveshell.py", line 3326, in run_code
  exec(code_obj, self.user_global_ns, self.user_ns)
 File "<ipython-input-6-d602d89ed0e7>", line 19, in <module>
  e.call(attr_err)
 File "<ipython-input-5-1b07c576630b>", line 15, in __exit__
  raise self.last_err
 File "<ipython-input-5-1b07c576630b>", line 19, in call
  func(*args, **kwargs)
 File "<ipython-input-6-d602d89ed0e7>", line 13, in attr_err
  raise AttributeError('x')
AttributeError: x

from contextlib import ExitStack


with ExitStack() as stack:
  stack.callback(type_err)
  stack.callback(value_err)
  stack.callback(attr_err)