[Python-Dev] ConfigParser mangles keys with special chars

[Steven D'Aprano]

On Fri, Apr 25, 2014 at 12:46:42PM -0400, Fred Drake wrote:
> On Fri, Apr 25, 2014 at 10:22 AM, Florian Bruhin <me at the-compiler.org> wrote:
> > While it seems ConfigParser doesn't do any escaping as all, I'm
> > thinking it should at least raise some exception when such a value is
> > trying to be set.
> >
> > I'd expect writing something and then reading it back via the same
> > configparser to *always* result in the same data, as long as writing
> > worked without error.
> >
> > Thoughts? Should I submit a bug report?
> 
> I believe you should, if only to provide a place to record why no
> change gets made.
> 
> Had ConfigParser been more careful from the beginning, that would have
> been really good.
> 
> At this point, it would be a backward-incompatible change, so it's
> unlikely such a change could be allowed to affect existing code.


It seems to me that the current behaviour is a bug and should be fixed. 
I think the relevant part of the docs is the part following the 
"comment_prefixes" and "inline_comment_prefixes" section:

   Please note that config parsers don’t support escaping of comment 
   prefixes so using inline_comment_prefixes may prevent users from 
   specifying option values with characters used as comment prefixes.
   When in doubt, avoid setting inline_comment_prefixes. In any 
   circumstances, the only way of storing comment prefix characters 
   at the beginning of a line in multiline values is to interpolate 
   the prefix, for example: ...


This is *seriously* underspecified, which is a bug in itself: option 
*values* don't support including inline_comment_prefixes, but do option 
*keys* support them? How about keys beginning with comment_prefixes? The 
specification doesn't say, but nor does it say that it's undefined 
behaviour.

I think that a line beginning with "#spam" is ambiguous, it isn't clear 
if it is intended as a comment "spam" or a key starting with #, so by 
the Zen, configparser should refuse to guess.


-- 
Steven