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pythonpython-3.xtraceback

Python print last traceback only?


Consider the following code and traceback:

>>> try:
...  raise KeyboardInterrupt
... except KeyboardInterrupt:
...  raise Exception
... 
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
KeyboardInterrupt

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
Exception
>>> 

I'd like to print only the most recent traceback (the one in which Exception was raised).
How can this be achieved?


From the above example, I'd like to print the following, as if raise Exception had been called outside the except clause.

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
Exception

Solution

  • The perfect question for me.

    You can suppress the exception context, that is the first part of the traceback, by explicitly raising the exception from None:

    >>> try:
            raise KeyboardInterrupt
        except:
            raise Exception from None
    
    Traceback (most recent call last):
      File "<pyshell#4>", line 4, in <module>
        raise Exception from None
    Exception
    

    This was formalized in PEP 409 and further improved in PEP 415. The original bug request for this was filed by myself btw.


    Note that suppressing the context will not actually remove the context from the new exception. So you can still access the original exception:

    try:
        try:
            raise Exception('inner')
        except:
            raise Exception('outer') from None
    except Exception as e:
        print(e.__context__) # inner