错误处理机制

异常捕获

try、except、else、finally

try:
    print('try...')
    r = 10 / int('2')
    print('result:', r)
except ValueError as e:
    print('ValueError:', e)
except ZeroDivisionError as e:
    print('ZeroDivisionError:', e)
else:
    print('no error!')
finally:
    print('finally...')
print('END')
# try... no error  finally  end

调用栈

# err.py:
def foo(s):
    return 10 / int(s)
def bar(s):
    return foo(s) * 2
def main():
    bar('0')
main()

运行程序结果如下，根据错误调用链，最终错误在line3

Traceback (most recent call last):
  File "err.py", line 11, in <module>
    main()
  File "err.py", line 9, in main
    bar('0')
  File "err.py", line 6, in bar
    return foo(s) * 2
  File "err.py", line 3, in foo
    return 10 / int(s)
ZeroDivisionError: division by zero

异常抛出

• 标准异常 | 异常名称 | 描述 | | —- | —- | | BaseException | 所有异常的基类 | | Exception | 继承于BaseException，常规错误的基类 | | StandardError | 继承于Exception，所有的内建标准异常的基类 |

• 抛出标准异常 ```python try: 1/0 except Exception as e: raise e

ZeroDivisionError: integer division or modulo by zero

- 抛出原样信息 
raise 不带参数时可抛出原样异常，会层级向上追溯错误
```python
try:
    1/0
except Exception as e:
    raise 
# ZeroDivisionError: integer division or modulo by zero

• 自定义错误信息 ```powershell

  raise Exception(“test”)

Traceback (most recent call last): File ““, line 1, in Exception: test ```

• 自定义错误类