Python raise 單獨一行的含義

在Python3中，單獨的raise會重新觸發前一個異常, 如果之前沒有觸發異常, 觸發RuntimeError。

In [1]: try:
   ...:     1/0
   ...: except ZeroDivisionError:
   ...:     raise
   ...:
---------------------------------------------------------------------------
ZeroDivisionError                         Traceback (most recent call last)
<ipython-input-1-758acd4e90aa> in <module>
      1 try:
----> 2     1/0
      3 except ZeroDivisionError:
      4     raise
      5

ZeroDivisionError: division by zero

在框架中，常常以下面的形式出現

In [1]: try:
   ...:     1/0
   ...: except:
   ...:     raise
   ...:
---------------------------------------------------------------------------
ZeroDivisionError                         Traceback (most recent call last)
<ipython-input-1-a69156c10f2c> in <module>
      1 try:
----> 2     1/0
      3 except:
      4     raise
      5

ZeroDivisionError: division by zero

參考：

https://docs.python.org/3.7/reference/simple_stmts.html#the-raise-statement