[Python-ideas] A directive for indentation type, stricter indentation parsing.

[Brett Cannon]

On Mon, Mar 25, 2019 at 9:33 AM Mikhail V <mikhailwas at gmail.com> wrote:

> Not a proposal yet, but some thoughts:
> I think it would help in a longer perspective if a user could
> include a directive in the header of the source code file that
> defines indentation character(s) for this source file. So this
> source would be parsed strictly by this char (or sequence).
>

This is more of a linter thing than a language thing, so I would propose
you take it to the code-quality mailing list.

-Brett


>
> E.g.:
>
>     # indent "\t"
>     ...
>
> Would force the Python parser to use exactly 1 tab for 1 indent level.
>
>     # indent "    "
>     ...
>
> Would accordingly force the parser to use exactly 4 spaces for
> 1 indent level.
>
> Frankly I don't have much proof in hand for that will be a good
> addition, but intuitively I suppose it would help with some possible
> future features and in general, ease the development of source
> processors.
>
> One possible example: if a potential future feature would require
> a statement, and moreover require it to be indentation-aware?
> Lets take e.g. a multi-line string:
>
>     s = """
>         Hello
>         world
>         """
>     print (s)
>
>     >>>
>
>         Hello
>         world
>
>
> Here it is not so intuitive (unless you already know) how the string would
> be parsed (given that Python blocks are actually indentation-based).
> So if one would want to try introduce a new indent-aware string type and
> look into possible parsing disambiguation scenarios - it will be not an
> easy task.
> E.g. say one proposes a syntax for auto-unindented string block:
>
>     s = !!!
>         Hello
>         world
>     print (s)
>     >>>
>     Hello
>     world
>
> (no leading newline, no leading indent in resulting string, which is a bit
> more
> expected result IMO).
>
> Then it seems one can define the parsing rule unambiguously _only_
> if one has a strictly defined character sequence for the indent level
> (e.g.  1 tab or 4 spaces, but not both).
> Thus it seems such a directive would be a prerequisite for such feature.
>
> And in general, I think it could help to make automatic conversions from
> one
> type of indentation to other easier.
>
>
>
> Mikhail
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