raise 与 raise ... from 的区别

起步Python 的 raise 和 raise from 之间的区别是什么？try: print(1 / 0)except Exception as exc: raise RuntimeError(“Something bad happened”)输出：Traceback (most recent call last): File “test4.py”, line 2, in <module> print(1 / 0)ZeroDivisionError: division by zeroDuring handling of the above exception, another exception occurred:Traceback (most recent call last): File “test4.py”, line 4, in <module> raise RuntimeError(“Something bad happened”)RuntimeError: Something bad happened而 raise from ：try: print(1 / 0)except Exception as exc: raise RuntimeError(“Something bad happened”) from exc输出：Traceback (most recent call last): File “test4.py”, line 2, in <module> print(1 / 0)ZeroDivisionError: division by zeroThe above exception was the direct cause of the following exception:Traceback (most recent call last): File “test4.py”, line 4, in <module> raise RuntimeError(“Something bad happened”) from excRuntimeError: Something bad happened分析不同之处在于，from 会为异常对象设置 cause 属性表明异常的是由谁直接引起的。处理异常时发生了新的异常，在不使用 from 时更倾向于新异常与正在处理的异常没有关联。而 from 则是能指出新异常是因旧异常直接引起的。这样的异常之间的关联有助于后续对异常的分析和排查。from 语法会有个限制，就是第二个表达式必须是另一个异常类或实例。如果在异常处理程序或 finally 块中引发异常，默认情况下，异常机制会隐式工作会将先前的异常附加为新异常的 context 属性。当然，也可以通过 with_traceback() 方法为异常设置上下文 context 属性，这也能在 traceback 更好的显示异常信息。raise Exception(“foo occurred”).with_traceback(tracebackobj)禁止异常关联from 还有个特别的用法：raise … from None ，它通过设置 suppress_context 属性指定来明确禁止异常关联：try: print(1 / 0)except Exception as exc: raise RuntimeError(“Something bad happened”) from None输出：Traceback (most recent call last): File “test4.py”, line 4, in <module> raise RuntimeError(“Something bad happened”) from NoneRuntimeError: Something bad happened总结在异常处理程序或 finally 块中引发异常，Python 会为异常设置上下文，可以手动通过 with_traceback() 设置其上下文，或者通过 from 来指定异常因谁引起的。这些手段都是为了得到更友好的异常回溯信息，打印清晰的异常上下文。若要忽略上下文，则可以通过 raise … from None 来禁止自动显示异常上下文。参考https://docs.python.org/3/ref…https://docs.python.org/3/lib...PEP 3109 – Raising Exceptions in Python 3000PEP 3134 – Exception Chaining and Embedded Tracebacks