[issue25436] argparse.ArgumentError missing error message in __repr__

[Daniel Fortunov]

Daniel Fortunov  added the comment:

As Paul points out, Python 3 gives a more sensible default repr so this becomes 
a non-issue.

Closing...

--
stage: patch review -> resolved
status: open -> closed
versions: +Python 2.7 -Python 3.4, Python 3.5, Python 3.6

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25436] argparse.ArgumentError missing error message in __repr__

[Daniel Fortunov]

Daniel Fortunov added the comment:

Paul,

Thanks for your comprehensive reply. I agree with everything you've said and 
the reason I've taken so long to reply is that I've been racking my brains to 
remember exactly how I came across this scenario.

I did at some point see an ArgumentError but I've forgotten the exact scenario. 
Since I can't see any of our internal codebase explicitly raising an 
ArgumentError, then I can only assume this must have just been a frustration I 
encountered when debugging into argparse code.

So I'll reformulate the question: Do you think it's worthwhile to make 
ArgumentError's repr() more useful for the purposes of interactive debugging 
alone?

Regards,
Dani

PS: I agree with your suggestion that you could achieve the same effect by 
defining a `__repr__` method for `ArgumentError`. I just thought that calling 
`super()` was more idiomatic.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25436] argparse.ArgumentError missing error message in __repr__

[paul j3]

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

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25436] argparse.ArgumentError missing error message in __repr__

[Berker Peksag]

Changes by Berker Peksag :


--
nosy: +berker.peksag
stage:  -> patch review
type:  -> behavior
versions: +Python 3.4, Python 3.5, Python 3.6

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue25436] argparse.ArgumentError missing error message in __repr__

[Daniel Fortunov]

New submission from Daniel Fortunov:

ArgumentError's __init__() fails to call super(), meaning
that the base exception doesn’t get a message, and thus repr() always
returns “argparse.ArgumentError()” with no message.

Not very helpful if that repr gets logged, or included in another error message 
:-(

I've attached a patch that fixes this, and adds corresponding tests.

--
components: Library (Lib)
files: cpython_ArgumentError_repr.patch
keywords: patch
messages: 253160
nosy: dfortunov
priority: normal
severity: normal
status: open
title: argparse.ArgumentError missing error message in __repr__
Added file: http://bugs.python.org/file40813/cpython_ArgumentError_repr.patch

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com