paul j3 added the comment:
The short `repr` is produced in Python2.7, but not 3.5.
Your test case:
action = argparse._StoreAction(['--file], dest='file_path')
error = argparse.ArgumentError(action, 'File not found.')
print(str(error))
print(repr(error))
With Python3.5 this displays:
argument --file: File not found.
ArgumentError(_StoreAction(option_strings=['--file'],
dest='file_path', nargs=None, const=None, default=None,
type=None, choices=None, help=None, metavar=None),
'File not found.')
In Python2.7 the `repr()` produces:
ArgumentError()
Your patch changes the `repr` to:
ArgumentError('File not found.', '--file')
I think you could achieve the same effect by defining a `__repr__` method for
`ArgumentError`.
By the way, to produce such an Action, you would normally use:
parser.add_argument('--file')
'--file=/foo/bar' is not a good argument option flag. The code may accept it,
but it will confuse your users.
--------------
Normally an `ArgumentError` is raised during parsing, and is caught at the end
of `parse_known_args` with:
except ArgumentError:
err = _sys.exc_info()[1]
self.error(str(err))
So its `str()` is passed on the the `parser.error` method (and on to
`parser.exit`). Normally a user, or developer's code will not see this error
class.
The purpose of `ArgumentError` is to clearly identify a class of error, and to
add the `Action` identity to the error message. It's part of the API so custom
Action classes can use it to pass errors through the normal parsing error
system.
Can you make a better case for needing an improved `repr`? How would it be
logged or otherwise be made visible to users and/or developers?
----------
nosy: +paul.j3
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<http://bugs.python.org/issue25436>
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