[issue32832] doctest should support custom ps1/ps2 prompts

[Cheryl Sabella]

Cheryl Sabella  added the comment:

Thank you for the suggestion, but per the discussion with Tim, I am closing as 
rejected.

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nosy: +cheryl.sabella
resolution:  -> rejected
stage: patch review -> resolved
status: open -> closed

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[issue32832] doctest should support custom ps1/ps2 prompts

[Sergey B Kirpichev]

Sergey B Kirpichev  added the comment:

> They support _more than one_ set of PS1/PS2 conventions.

I saw this, not sure if that's required.  IMHO, same effect should be possible 
by running doctest several times with different conventions.

> Who would it help?

In principle, any project, that uses some custom shell (i.e. IPython) per 
default.  I believe, "easily understood tests" should start with prompts that 
users could easily recognise.

> Something that might change my mind:  find an author of a widely used 
> alternative Python shell who says this change would allow them to _remove_ 
> their own doctest-PS1/PS2 customization code.  That would be a real use case.

I admit, exactly this use case I can't provide right now.

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[issue32832] doctest should support custom ps1/ps2 prompts

[Tim Peters]

Tim Peters  added the comment:

You missed my point about IPython:  forget "In/Out arrays, etc".  What you 
suggest is inadequate for _just_ changing PS1/PS2 for IPython.  Again, read 
their `parse()` function.  They support _more than one_ set of PS1/PS2 
conventions.  So the code changes you suggest wouldn't help them.  So long as 
they want to support more than one set, they'd still have to write their own 
`parse()` function just to deal with multiple PS1/PS2 conventions.

For the rest, it's not the number of people using non-CPython shells that's 
rare, but the number _of_ non-CPython shells.  IPython is popular, they already 
solved their problem, and the patch wouldn't help them anyway.  Who would it 
help?

I don't take "a plain CPython shell with customized ps1/ps2" seriously because, 
as I said, after some decades now I still don't know of anyone who does that 
(granting that newbies sometimes try it, go 'ha! ha! - cool!", and never try it 
again).  If any such people exist, I would oppose changing doctest just for 
them, because the _point_ of doctest is to help write easily understood tests.  
Catering to changing shell syntax in random ways opposes that goal - 
programming is a social activity.

So, sorry, but I remain opposed.  Something that might change my mind:  find an 
author of a widely used alternative Python shell who says this change would 
allow them to _remove_ their own doctest-PS1/PS2 customization code.  That 
would be a real use case.

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[issue32832] doctest should support custom ps1/ps2 prompts

[Sergey B Kirpichev]

Sergey B Kirpichev  added the comment:

> are people writing an entirely different shell interface.  They're rare.

Or just using a different shell interface.  Or even different defaults for the 
standard shell...

And they are not rare.  Almost nobody in reality use CPython shell - that's 
definitely true for scientific applications of Python, data scientists, etc.

> As your IPython example showed, their job is harder than _just_ replacing 
> PS1/PS2.

Yes, custom shells have much more stuff (In/Out arrays, etc), but changing 
PS1/PS2 - require very tiny modifications for doctest.  And such changes - 
almost all that usually prevent using standard doctest for testing examples, 
written for applications, which assume "a different shell interface" (which, I 
remind, may be just a plain CPython shell with customized ps1/ps2).

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[issue32832] doctest should support custom ps1/ps2 prompts

[Tim Peters]

Tim Peters  added the comment:

Sergey, I understand that, but I don't care.  The only people I've ever seen 
_use_ this are people writing an entirely different shell interface.  They're 
rare.  There's no value in complicating doctest to cater to theoretical use 
cases that don't exist - to the contrary, that's counterproductive complication.

As your IPython example showed, their job is harder than _just_ replacing 
PS1/PS2.  See their `parse()` function.  They want to cater both to IPython's 
PS1/PS2 conventions _and_ to the standard CPython terminal shell PS1/PS2 
conventions.

But they don't cater to _more_ than just those either.  Why should they?  Same 
thing here:  extra complication for no good reason.

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[issue32832] doctest should support custom ps1/ps2 prompts

[Sergey B Kirpichev]

Sergey B Kirpichev  added the comment:

> doctest was intended to deal with the standard CPython terminal shell.  I'd 
> like to keep it that way

The point is: ps1/ps2 customization could be considered as part of the standard 
shell.  If stdlib allow such changes - doctest module should take this into 
account.

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[issue32832] doctest should support custom ps1/ps2 prompts

[Tim Peters]

Tim Peters  added the comment:

doctest was intended to deal with the standard CPython terminal shell.  I'd 
like to keep it that way, but recognize that everyone wants to change 
everything into "a framework" ;-)

How many other shells are there?  As Sergey linked to, IPython already dealt 
with its shell conventions, and PS1/PS2 differences account for a relatively 
tiny amount of the 600+ lines of IPython-customization code they'd need anyway. 
 That is, I don't see that this would be of much value to IPython.

So people who "need" this already figured out how to do this - and there aren't 
many of them anyway.  I'd leave it alone.

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[issue32832] doctest should support custom ps1/ps2 prompts

[Raymond Hettinger]

Raymond Hettinger  added the comment:

Tim, what do you say, feature or feature creep, straightforward patch or can of 
worms?

--
assignee:  -> tim.peters
nosy: +rhettinger, tim.peters
type:  -> enhancement
versions: +Python 3.8

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[issue32832] doctest should support custom ps1/ps2 prompts

[Roundup Robot]

Change by Roundup Robot :


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keywords: +patch
pull_requests: +6775
stage:  -> patch review

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[issue32832] doctest should support custom ps1/ps2 prompts

[Sergey B Kirpichev]

New submission from Sergey B Kirpichev :

The Python stdlib allows override of sys.ps1/ps2 (to make IPython-like dynamic 
prompts and so on).  I believe it would be a good idea to
support this in doctest too, to cover cases when given application
uses different from defaults settings for the interpreter.

Probably, we could add ps1/2 optional arguments for DoctestParser.__init__().

Some projects already patch doctest module for this, e.g. IPython:
https://github.com/ipython/ipython/blob/master/IPython/testing/plugin/ipdoctest.py
It shouldn't be too hard to port this feature.

--
components: Library (Lib)
messages: 312053
nosy: Sergey.Kirpichev
priority: normal
severity: normal
status: open
title: doctest should support custom ps1/ps2 prompts

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