New submission from Roy Hyunjin Han: Exceptions and arguments disappear when using argparse inside a "with" statement. The behavior was confusing and frustrating because I could not pinpoint why certain arguments were missing or unrecognized.
Unhandled exceptions inside the with statement typically trigger a traceback, unless __exit__ returns True, in which the exception is "swallowed" (https://www.python.org/dev/peps/pep-0343/). However, the NameError exception and tile_indices argument disappear because of a premature sys.exit (https://hg.python.org/cpython/file/default/Lib/argparse.py#l2385). ``` """ $ python exception-in-with.py EXPECTED Traceback (most recent call last): File "exception-in-with.py", line 51, in <module> abc # !!! NameError: name 'abc' is not defined ACTUAL usage: exception-in-with.py [-h] --image_path PATH exception-in-with.py: error: argument --image_path is required $ python exception-in-with.py --image_path x EXPECTED == ACTUAL Traceback (most recent call last): File "exception-in-with.py", line 51, in <module> abc # !!! NameError: name 'abc' is not defined $ python exception-in-with.py --image_path x --tile_indices 1 EXPECTED Traceback (most recent call last): File "exception-in-with.py", line 51, in <module> abc # !!! NameError: name 'abc' is not defined ACTUAL usage: exception-in-with.py [-h] --image_path PATH exception-in-with.py: error: unrecognized arguments: --tile_indices 1 """ from argparse import ArgumentParser class Starter(object): def __init__(self): self.argument_parser = ArgumentParser() def __enter__(self): return self def __exit__(self, exception_type, exception_value, exception_traceback): self.argument_parser.parse_args() def add_argument(self, *args, **kw): self.argument_parser.add_argument(*args, **kw) with Starter() as starter: starter.add_argument('--image_path', metavar='PATH', required=True) abc # !!! starter.add_argument('--tile_indices', metavar='INTEGER') ``` ---------- components: Library (Lib) files: argparse-with-exception.py messages: 242192 nosy: invisibleroads priority: normal severity: normal status: open title: Exceptions and arguments disappear when using argparse inside with statement type: behavior versions: Python 2.7, Python 3.3 Added file: http://bugs.python.org/file39227/argparse-with-exception.py _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue24070> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
