[issue24338] In argparse adding wrong arguments makes malformed namespace

[Irit Katriel]

Irit Katriel  added the comment:

>From the discussion and "rejected" resolution it looks like the intention was 
>to close this issue. I will do that soon if nobody objects.

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nosy: +iritkatriel
status: open -> pending

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


Removed file: https://bugs.python.org/file48470/126.pdf

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[tomas platz]

Change by tomas platz :


Added file: https://bugs.python.org/file48470/126.pdf

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[paul j3]

paul j3 added the comment:

http://bugs.python.org/issue15125
argparse: positional arguments containing - in name not handled well

Discussion on whether positionals 'dest' should translate '-' to '_'.

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[py.user]

py.user added the comment:

paul j3 wrote:
 It's an attempt to turn such flags into valid variable names.

I'm looking at code and see that he wanted to make it handy for use in a 
resulting Namespace.

args = argparse.parse_args(['--a-b-c'])
abc = args.a_b_c

If he doesn't convert, he cannot get attribute without getattr().

It's not a UNIX reason.

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[paul j3]

paul j3 added the comment:

Yes, the '_' makes it accessible as an attribute name.  But the presence of '-' 
in the option name has a UNIX history.  That is a flag like '--a-b-c' is 
typical, '--a_b_c' is not.

There is less of precedent for a flag like '@@a@b' or '--a@b'.

Here's the relevant code from '_ActionContainer' class.

def _get_optional_kwargs(self, *args, **kwargs):
# determine short and long option strings
...
for option_string in args:
# error on strings that don't start with an appropriate prefix
if not option_string[0] in self.prefix_chars:
...
raise ValueError(msg % args)

# strings starting with two prefix characters are long options
option_strings.append(option_string)
if option_string[0] in self.prefix_chars:
if len(option_string)  1:
if option_string[1] in self.prefix_chars:
long_option_strings.append(option_string)

# infer destination, '--foo-bar' - 'foo_bar' and '-x' - 'x'
dest = kwargs.pop('dest', None)
if dest is None:
if long_option_strings:
dest_option_string = long_option_strings[0]
else:
dest_option_string = option_strings[0]
dest = dest_option_string.lstrip(self.prefix_chars)
if not dest:
msg = _('dest= is required for options like %r')
raise ValueError(msg % option_string)
dest = dest.replace('-', '_')

Even if you need to have odd ball characters in the option flag, you don't have 
to settle for them in the 'dest'.  You can always give the argument a nice 
looking 'dest'.  

That's a rather common pattern in 'argparse'.  Provide a default handling for 
common cases, and provide parameters that let the user override those defaults. 
 The net effect is to limit the complexity of the code, while increasing the 
complexity of the documentation.

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[paul j3]

paul j3 added the comment:

The code that converts '-' to '_' is independent of the code that uses 
'prefix_chars'.

The '-' conversion handles a long standing UNIX practice of allowing that 
character in the middle of option flags.  It's an attempt to turn such flags 
into valid variable names.  There is a bug/issue about whether the conversion 
should be applied to positional argument 'dest' parameters.  

Is the use of other funny characters in optional flags common enough to warrant 
a patch?  It probably wouldn't be hard to convert all 'prefix_chars' to '_'.  
But should it still convert '-', even if it isn't in that list?  What about 
users who are content with using 'getattr', and don't want the conversion?

Note also that you can invoke `parse_args` with your own custom Namespace 
object.

https://docs.python.org/3.4/library/argparse.html#the-namespace-object

This means you can write a Namespace class alternative that can handle funny 
characters in any way you want.  I discuss the use of custom Namespace classes 
in http://bugs.python.org/issue9351.

Between the availability of 'getattr' and namespace customization, I don't 
think there's anything here that requires a patch.  But I'm in favor of keeping 
the issue open for discussion.

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[Matthias Bussonnier]

Matthias Bussonnier added the comment:

Minimal changes to the repr seem to work.
I can submit a proper patch.

class N2(Namespace):

def __repr__(self):
type_name = type(self).__name__
arg_strings = []
unarg={}
for arg in self._get_args():
arg_strings.append(repr(arg))
for name, value in self._get_kwargs():
if name.isidentifier():
arg_strings.append('%s=%r' % (name, value))
else:
unarg[name] = value
if unarg:
r_unarg = ', **%s' %(repr(unarg))
else:
r_unarg = ''
return '%s(%s%s)' % (type_name, ', '.join(arg_strings), r_unarg)

 N2(a=1, b=2, **{single ' quote :', 'double  quote':''})
N = N2(a=1, b=2, **{single ' quote :', 'double  quote':''})

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[Matthias Bussonnier]

Matthias Bussonnier added the comment:

Maybe the __repr__ of _AttributeHolder should be changed so that invalid args 
are shown as unpacked dict in the signature ?

Something that would :

 argparse.Namespace(**{'foo bar':1})
argparse.Namespace(**{'foo bar':1})

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[py.user]

py.user added the comment:

Serhiy Storchaka wrote:
 for example the use of such popular options as -0 or -@

Ok.

What about inconsistent conversion dashes to underscores?

 import argparse
 
 parser = argparse.ArgumentParser(prefix_chars='@')
 _ = parser.add_argument('--x-one-two-three@')
 _ = parser.add_argument('@@y-one-two-three@')
 args = parser.parse_args(['abc'])
 args
Namespace(--x-one-two-three@='abc', y_one_two_three@=None)


We set dash as non-option char, but it continues to convert to underscore while 
another option char doesn't convert.

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[py.user]

New submission from py.user:

 import argparse
 
 parser = argparse.ArgumentParser()
 _ = parser.add_argument('foo bar')
 _ = parser.add_argument('--x --y')
 args = parser.parse_args(['abc'])
 
 args
Namespace(foo bar='abc', x __y=None)
 
 'foo bar' in dir(args)
True
 'x __y' in dir(args)
True


Passing wrong arguments silently makes a namespace which attributes are not 
accessible.

ISTM, add_argument() should raise a ValueError exception.

--
components: Library (Lib)
messages: 244534
nosy: py.user
priority: normal
severity: normal
status: open
title: In argparse adding wrong arguments makes malformed namespace
type: behavior
versions: Python 3.4, Python 3.5

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[issue24338] In argparse adding wrong arguments makes malformed namespace

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

They are accessible.

 getattr(args, 'foo bar')
'abc'

The limitation that argument names should be Python identifiers is too strong 
and adding it will break existing code (for example the use of such popular 
options as -0 or -@).

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nosy: +serhiy.storchaka
resolution:  - rejected
status: open - pending

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