[Python-ideas] Transportable indent level markers. >>>===<<<

Ron Adam ron3200 at gmail.com
Thu Dec 15 08:06:21 CET 2011

On Thu, 2011-12-15 at 15:25 +1000, Nick Coghlan wrote:
> On Thu, Dec 15, 2011 at 3:09 PM, Ron Adam <ron3200 at gmail.com> wrote:
> > Lets say you are going to past in several locations in a file and those
> > locations may have different indent levels.  How would you write that
> > using your suggestion so you don't have to change it in anyway for it to
> > work.
> >
> > With my suggestion, that would just work no matter the source file
> > indent level. (*)  All you need is the line numbers to insert it at.  I
> > think with your idea, you would also need a place holder of some type.
> OK, I at least understand what you're trying to do now. However, I
> don't think you have a valid use case. What would a templating
> language based on your notation look like?

Any program that can patch text files together.  As to how it does it,
it probably would use a script of some sort.  This would just make it
easier to by offering a way around indenting issues.

Another use case is it makes transmitting python compatible code easier
in a web page or email.  The braces version would do that also.  I think
it could make python a bit more attractive for things like that.  Where
a app is transmitted and run at the destination.   There are still the
security issues to work out, but this would knock down one domino in
that direction.

For example they don't have to event ways to avoid the white space
munging.  Python could be represented as code blocks that might look

 <pycode = ";;; for x in items: \\\ sum = op(x) ;;; if sum > MAX:
 \\\ break">

Except much longer.  In this case there isn't a need for it to be
pretty. But there is a need for it to work correctly.

I was thinking it might be possible to have the python shell echo the
indent markes in the left side as it scroll lines up. Replacing the
'>>>' and '...' with the respective markes as you enter the lines.  And
it could also take these if they are pasted in.  Cutting and pasting
from one shell to another could work in that case.

As far as unglyness goes... is it really that bad?  you can leave the
white space in.  The indent hints are used not the spaces in this case.

  ;;; for x in items:
  \\\     sum = op(x)
  ;;;     if sum > MAX:
  \\\         break

And keep in mind that this isn't something you will see in normal use.
It's just available for when its needed.  But if you run across code
like this it will still work.  Nothing special would need to be done to
make it work.

> How would you extend it to
> implement multi-line lambdas?

As I said, it doesn't change the language at all.  So extending lambda
is not in the scope of this topic.  That would be something new and
should be done separately in any case.

> If you can't cleanly do those two
> things, who cares if it lets you copy and paste snippets at arbitrary
> points in a Python file? What's the *functional* pay-off for the
> ugliness?

? See above.

> (And I freely admit that my suggestion is also quite ugly. However,
> the status quo, with everyone inventing assorted templating languages
> for use with Python that are largely independent of Python itself
> already sucks)

If it was a big patch to many files, I would say it isn't worth it.
But it would be a very small patch to only one file and wouldn't change
the grammer, ast, or anything else.  It's almost free.

I think it may have a nice benefit for very little effort. But I think
we should just wait a bit and see if there is more interest first.


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