IPython - Hide traceback when SystemExit is raised - ipython

Question

I'm surprised no one asked this issue before, but somehow I couldn't find an answer.
When raising SystemExit in a simple my_script.py.
import sys
sys.exit(2)
No traceback is displayed when running python my_script.py, as explained in python doc:
SystemExit: When it is not handled, the Python interpreter exits; no stack traceback is printed.
However when running with ipython, a traceback is printed:
$ ipython my_script.py
---------------------------------------------------------------------------
SystemExit Traceback (most recent call last)
my_script.py in <module>
2 import sys
3
----> 4 sys.exit(2)
SystemExit: 2
This is an issue when using argparse as parser.parse_args() call sys.exit() if parsing fail. So user see an unhelpful SystemExit: 2 rather than the error message printed above the traceback.
A workaround is to use os._exit but this feels very hacky and might not properly cleanup.
Is there a ipython flag which would silence/hide the traceback when SystemExit is raised, like with standard python interpreter ?

Answer 1

Here's a sample session with xmode 'plain':
In [1]: import argparse
In [2]: parser=argparse.ArgumentParser()
In [3]: parser.add_argument('foo')
Out[3]: _StoreAction(option_strings=[], dest='foo', nargs=None, const=None, default=None, type=None, choices=None, help=None, metavar=None)
In [4]: import sys; sys.argv
Out[4]:
['/usr/local/bin/ipython3',
'--pylab',
'qt',
'--nosep',
'--term-title',
'--InteractiveShellApp.pylab_import_all=False',
'--TerminalInteractiveShell.xmode=Plain']
In [5]: parser.parse_args()
usage: ipython3 [-h] foo
ipython3: error: unrecognized arguments: --pylab --nosep --term-title --InteractiveShellApp.pylab_import_all=False --TerminalInteractiveShell.xmode=Plain
An exception has occurred, use %tb to see the full traceback.
SystemExit: 2
/usr/local/lib/python3.8/dist-packages/IPython/core/interactiveshell.py:3426: UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.
warn("To exit: use 'exit', 'quit', or Ctrl-D.", stacklevel=1)
In [6]: parser.parse_args([])
usage: ipython3 [-h] foo
ipython3: error: the following arguments are required: foo
An exception has occurred, use %tb to see the full traceback.
SystemExit: 2
/usr/local/lib/python3.8/dist-packages/IPython/core/interactiveshell.py:3426: UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.
warn("To exit: use 'exit', 'quit', or Ctrl-D.", stacklevel=1)
This shows the error message produced by the parser, followed by the capture and traceback. This allows me to continue interactively.
With plain interpreter, I get the message followed by an exit.
2310:~/mypy$ python3
Python 3.8.5 (default, Jan 27 2021, 15:41:15)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import argparse
>>> parser=argparse.ArgumentParser()
>>> parser.add_argument('foo');
_StoreAction(option_strings=[], dest='foo', nargs=None, const=None, default=None, type=None, choices=None, help=None, metavar=None)
>>> parser.parse_args()
usage: [-h] foo
: error: the following arguments are required: foo
2311:~/mypy$
For me the whole purpose of using ipython is to try multiple things, without it quitting on me. Otherwise I'd run the script without the interactive layer.