[issue40265] argparse.Namespace __repr__ does not handle reserved keywords

[Raymond Hettinger]

Raymond Hettinger  added the comment:

Saiyang, thank you for the suggestion, but I'm going to decline.  The other 
referenced issue had to do with readability of otherwise incomprehensible 
output and that's what made it worthwhile.  In this issue, you're prioritizing 
round-tripping at the expense of readability.  To me, that is a step backwards. 
 Since people don't normally run eval() on the repr() of a Namespace, 
round-tripping should take a backseat to readability.  And, as you noted, there 
is already an option to set *dest* if needed.

--
resolution:  -> rejected
stage:  -> resolved
status: open -> closed

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[issue40265] argparse.Namespace __repr__ does not handle reserved keywords

[Saiyang Gou]

Saiyang Gou  added the comment:

> The primary function of the Namespace class is to hold valid attributes and 
> to allow the dot operator to access those attributes.

I acknowledge this. Invalid attribute names are not useful in production. 
However, some crazy people like me would define arguments like these, producing 
an repr string that does not round-trip:

>>> from argparse import ArgumentParser
>>> parser = ArgumentParser()
>>> parser.add_argument('-8')
>>> parser.add_argument('-@')
>>> parser.add_argument('--return')
>>> parser.parse_args(['-8', 'y', '-@', 'a.com', '--return', 'foo'])
Namespace(return='foo', **{'8': 'y', '@': 'a.com'})

(I know I can use the `dest` argument to define an alternative name to store in 
the namespace.)

The reason why I open this issue is that I see issue 24360 already tried to 
improve the repr string for invalid names by using the `isidentifier` check. 
(Which is almost "as unuseful as this issue" for production use, since repr is 
almost only used for development instead of production.) The original author 
thought the improvement was enough to be round-trippable but missed the special 
case of keywords, and my patch will fix this.

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[issue40265] argparse.Namespace __repr__ does not handle reserved keywords

[Raymond Hettinger]

Raymond Hettinger  added the comment:

ISTM this a purely theoretical problem since "ns.return" is already a syntax 
error.

The primary function of the Namespace class is to hold valid attributes and to 
allow the dot operator to access those attributes.  Handling invalid attribute 
names is beyond its scope.

--
assignee:  -> rhettinger
nosy: +rhettinger

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[issue40265] argparse.Namespace __repr__ does not handle reserved keywords

[Saiyang Gou]

New submission from Saiyang Gou :

It is generally a convention to design the repr string such that 
`eval(repr(obj))` can reproduce the object. Issue 24360 handles the special 
situation when arg name passed to `argparse.Namespace` is not a valid 
identifier:

>>> from argparse import Namespace
>>> Namespace(**{')': 3})
Namespace(**{')': 3})

However there is one more corner case to handle: the arg name could be a 
reserved keyword.

>>> Namespace(**{'return': 3})
Namespace(return=3)
>>> Namespace(return=3)
  File "", line 1
Namespace(return=3)
  ^
SyntaxError: invalid syntax

I noticed that the documentation of `str.isidentifier` tells me to also check 
for keywords with `keyword.iskeyword`. However `__debug__` is not considered a 
keyword by `keyword.iskeyword`, but cannot be assigned to:

>>> keyword.iskeyword('__debug__')
False
>>> Namespace(**{'__debug__':3})
Namespace(__debug__=3)
>>> Namespace(__debug__=3)
  File "", line 1
SyntaxError: cannot assign to __debug__

I propose to enhance the arg name check in `argparse._AttributeHolder` from `if 
name.isidentifier():` to `if name.isidentifier() and not 
keyword.iskeyword(name) and name != '__debug__:'` to fix this. However this may 
slow down the argparse library since it will need to `import keyword` at the 
beginning, and `__repr__` will also be slower due to the added arg name checks.

By the way, when I came across issue 39076, I noticed that 
`types.SimpleNamespace` is not considering this problem at all:

>>> types.SimpleNamespace(**{')': 1, 'return': 2})
namespace()=1, return=2)

--
components: Library (Lib)
messages: 366265
nosy: gousaiyang
priority: normal
severity: normal
status: open
title: argparse.Namespace __repr__ does not handle reserved keywords
type: enhancement
versions: Python 3.9

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