Re: [Twisted-Python] Conch text attribute flattening quirks

[Jonathan Jacobs]

On Thu, Feb 23, 2012 at 16:12,   wrote:
> I think the behavior you observed is a bug in the implementation (I
> noticed it during our IRC conversation the other day as well, but wasn't
> sure if I'd made a mistake or misread something).  It should be fixed,
> and perhaps that TODO test made to pass. :)

Should I file a new ticket for this and do the work in a separate branch?

In terms of making the TODO test pass: Unless I'm mistaken it looks to
me that the render method (toVT102, toMIRCControlCode, etc.) will have
to be passed the current attribute state in order to determine what it
needs to emit to be most efficient. Do you see any better way to
achieve this?

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Re: [Twisted-Python] Conch text attribute flattening quirks

[exarkun]

On 22 Feb, 04:15 pm, jonathan+twis...@jsphere.com wrote:
>On Wed, Feb 22, 2012 at 17:25, Tim Allen  wrote:
>>...that is, there's no code for 'end bold' or 'end italics' (or blink, 
>>dim,
>>underline, invisible, any kind of colouring, etc.) just an 'end all
>>special attributes' code. Therefore it's reasonable for conch's helper
>>library to not handle nested formatting, since no terminal program 
>>will
>>produce such a thing, because it's impossible to represent in the
>>VT100/VT200 formatting language.
>
>I understand this, but then what is the point of placing content into
>A.bold in the first place? Why not just drop A.bold into a flat
>stream: [foo, A.bold, bar]

I think the behavior you observed is a bug in the implementation (I 
noticed it during our IRC conversation the other day as well, but wasn't 
sure if I'd made a mistake or misread something).  It should be fixed, 
and perhaps that TODO test made to pass. :)

Jean-Paul

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Re: [Twisted-Python] Conch text attribute flattening quirks

[Jonathan Jacobs]

On Wed, Feb 22, 2012 at 17:25, Tim Allen  wrote:
> ...that is, there's no code for 'end bold' or 'end italics' (or blink, dim,
> underline, invisible, any kind of colouring, etc.) just an 'end all
> special attributes' code. Therefore it's reasonable for conch's helper
> library to not handle nested formatting, since no terminal program will
> produce such a thing, because it's impossible to represent in the
> VT100/VT200 formatting language.

I understand this, but then what is the point of placing content into
A.bold in the first place? Why not just drop A.bold into a flat
stream: [foo, A.bold, bar]

What's more confusing is that there are a handful of tests that
describe this nesting and even test it, although none of them (except
for the one marked TODO, which fails because of the problem I've
described) actually test adding things to the parent level after
nesting an attribute.

> I guess an argument could be made that the helper function should track
> which attributes are enabled at any particular point in the string, and
> calculate the correct sequence of disable-everything/re-enable-the-
> remaining-attributes codes, but evidently nobody's needed such a thing
> before.

It's not actually even all that hard, there is nothing in particular
to additionally track if you don't mind being a little inefficient
about it, which is how the IRC code in #3844 does it.

-- 
Jonathan

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Re: [Twisted-Python] Conch text attribute flattening quirks

[Tim Allen]

On Wed, Feb 22, 2012 at 01:47:46PM +0200, Jonathan Jacobs wrote:
> >>> from twisted.conch.insults.helper import CharacterAttribute
> >>> from twisted.conch.insults.text import flatten, attributes as A
> >>> flatten(A.normal['hello', A.bold[' world '], 'quux'], 
> >>> CharacterAttribute())
> 'hello\x1b[1m world quux'
> 
> My expectations are that only " world " will be marked up with bold
> attributes, since it is the only piece of content in the "bold"
> attribute, while "hello" and "quux" both appear in normal text, i.e.
> without any additional markup. Looking at the output you can see that
> "hello" appears as normal text and then " world quux" appears in bold.

Since it's in twisted.conch, I'm guessing that this character-attribute
stuff is designed to model the VT100 character attribute system, rather
than some generic tree-of-strings-and-attributes. For example, somebody
used to the way HTML works might want to nest bold and italics like
this:

hello world quux

However, to achieve the same result on a traditional terminal (and using
the tput(1) command to produce the formatting codes), you'd have to do
something like this:

tput sitm   # enable italics
echo -n "hello "
tput bold   # enable bold
echo -n "world"
tput sgr0   # disable all special attributes
tput sitm   # enable italics again
echo " quux"

...that is, there's no code for 'end bold' or 'end italics' (or blink, dim,
underline, invisible, any kind of colouring, etc.) just an 'end all
special attributes' code. Therefore it's reasonable for conch's helper
library to not handle nested formatting, since no terminal program will
produce such a thing, because it's impossible to represent in the
VT100/VT200 formatting language.

I guess an argument could be made that the helper function should track
which attributes are enabled at any particular point in the string, and
calculate the correct sequence of disable-everything/re-enable-the-
remaining-attributes codes, but evidently nobody's needed such a thing
before.

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[Twisted-Python] Conch text attribute flattening quirks

[Jonathan Jacobs]

Hello,

I'm hoping to wrap up work on ticket #3844 [1] before the next release of 
Twisted, however there are a few quirks in the small DSL used for specifying 
text with attributes (see the ticket for some commentary on these.)

I decided to look more closely at what happens with Conch (which is where the 
DSL originally came from and has remained largely unchanged) in some of the 
places I was having problems with the IRC formatting. I was struck by something 
that looks like it is rather incorrect behaviour (on Twisted trunk as of 
2012/2/22 and Twisted 11.0.0 on Debian):

>>> from twisted.conch.insults.helper import CharacterAttribute
>>> from twisted.conch.insults.text import flatten, attributes as A
>>> flatten(A.normal['hello', A.bold[' world '], 'quux'], CharacterAttribute())
'hello\x1b[1m world quux'

My expectations are that only " world " will be marked up with bold attributes, 
since it is the only piece of content in the "bold" attribute, while "hello" 
and "quux" both appear in normal text, i.e. without any additional markup. 
Looking at the output you can see that "hello" appears as normal text and then 
" world quux" appears in bold.

Is this the expected behaviour? There are no tests that actually test this 
particular case, as far as I can tell, except for 
twisted.conch.test.test_text.EfficiencyTestCase but that is marked as "todo" 
(the tests themselves do indeed fail.) While the name of this test case 
indicates tests for efficient markup, as far as I can tell these tests also 
assume (and fail) that the structure is flattened the same way I was expecting.

Any guidance would be appreciated.

Regards

[1] 

-- 
Jonathan



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