HTML Parser which allows low-keyed local changes?

R

Robert

I tried lxml, but after walking and making changes in the element
tree, I'm forced to do a full serialization of the whole document
(etree.tostring(tree)) - which destroys the "human edited" format
of the original HTML code.
makes it rather unreadable.

is there an existing HTML parser which supports tracking/writing
back particular changes in a cautious way by just making local
changes? or a least tracks the tag start/end positions in the file?


Robert
 
S

Stefan Behnel

Robert, 31.01.2010 20:57:
I tried lxml, but after walking and making changes in the element tree,
I'm forced to do a full serialization of the whole document
(etree.tostring(tree)) - which destroys the "human edited" format of the
original HTML code. makes it rather unreadable.

What do you mean? Could you give an example? lxml certainly does not
destroy anything it parsed, unless you tell it to do so.

Stefan
 
R

Robert

Stefan said:
Robert, 31.01.2010 20:57:

What do you mean? Could you give an example? lxml certainly does not
destroy anything it parsed, unless you tell it to do so.

of course it does not destroy during parsing.(?)

I mean: I want to walk with a Python script through the parsed
tree HTML and modify here and there things (auto alt tags from
DB/similar, link corrections, text sections/translated
sentences... due to HTML code and content checks.)

Then I want to output the changed tree - but as close to the
original format as far as possible. No changes to my white space
identation, etc.. Only lokal changes, where really tags where
changed.

Thats similiar like that what a good HTML editor does: After you
made little changes, it doesn't reformat/re-spit-out your whole
code layout from tree/attribute logic only. you have lokal changes
only.
But a simple HTML editor like that in Mozilla-Seamonkey outputs a
whole new HTML, produces the HTML from logical tree only
(regarding his (ugly) style), destroys my whitspace layout and
much more - forgetting anything about the original layout.

Such a "good HTML editor" must somehow track the original
positions of the tags in the file. And during each logical change
in the tree it must tracks the file position changes/offsets. That
thing seems to miss in lxml and BeautifulSoup which I tried so far.

This is a frequent need I have. Nobody else's?

Seems I need to write my own or patch BS to do that extra tracking?


Robert
 
R

Robert

Robert said:
of course it does not destroy during parsing.(?)

I mean: I want to walk with a Python script through the parsed tree HTML
and modify here and there things (auto alt tags from DB/similar, link
corrections, text sections/translated sentences... due to HTML code and
content checks.)

Then I want to output the changed tree - but as close to the original
format as far as possible. No changes to my white space identation,
etc.. Only lokal changes, where really tags where changed.

Thats similiar like that what a good HTML editor does: After you made
little changes, it doesn't reformat/re-spit-out your whole code layout
from tree/attribute logic only. you have lokal changes only.
But a simple HTML editor like that in Mozilla-Seamonkey outputs a whole
new HTML, produces the HTML from logical tree only (regarding his (ugly)
style), destroys my whitspace layout and much more - forgetting
anything about the original layout.

Such a "good HTML editor" must somehow track the original positions of
the tags in the file. And during each logical change in the tree it must
tracks the file position changes/offsets. That thing seems to miss in
lxml and BeautifulSoup which I tried so far.

This is a frequent need I have. Nobody else's?

Seems I need to write my own or patch BS to do that extra tracking?

basic feature(s) of such parser perhaps:

* can it tell for each tag object in the parsed tree, at what
original file position start:end it resided? even a basic need:
tell me the line number e.g. (for warning/analysis reports e.g.)

(* do the tree objects auto track/know if they were changed. (for
convenience; a tree copy may serve this otherwise .. )

the creation of a output with local changes whould be rather
simple from that ...


Robert
 
S

Stefan Behnel

Robert, 01.02.2010 14:36:
of course it does not destroy during parsing.(?)

I meant "parsed" in the sense of "has parsed and is now working on".

I mean: I want to walk with a Python script through the parsed tree HTML
and modify here and there things (auto alt tags from DB/similar, link
corrections, text sections/translated sentences... due to HTML code and
content checks.)

Sure, perfectly valid use case.

Then I want to output the changed tree - but as close to the original
format as far as possible. No changes to my white space identation,
etc.. Only lokal changes, where really tags where changed.

That's up to you. If you only apply local changes that do not change any
surrounding whitespace, you'll be fine.

Thats similiar like that what a good HTML editor does: After you made
little changes, it doesn't reformat/re-spit-out your whole code layout
from tree/attribute logic only. you have lokal changes only.

HTML editors don't work that way. They always "re-spit-out" the whole code
when you click on "save". They certainly don't track the original file
position of tags. What they preserve is the content, including whitespace
(or not, if they reformat the code, but that's usually an *option*).

Such a "good HTML editor" must somehow track the original positions of
the tags in the file. And during each logical change in the tree it must
tracks the file position changes/offsets.

Sorry, but that's nonsense. The file position of a tag is determined by
whitespace, i.e. line endings and indentation. lxml does not alter that,
unless you tell it do do so.

Since you keep claiming that it *does* alter it, please come up with a
reproducible example that shows a) what you do in your code, b) what your
input is and c) what unexpected output it creates. Do not forget to include
the version number of lxml and libxml2 that you are using, as well as a
comment on /how/ the output differs from what you expected.

My stab in the dark is that you forgot to copy the tail text of elements
that you replace by new content, and that you didn't properly indent new
content that you added. But that's just that, a stab in the dark. You
didn't provide enough information for even an educated guess.

Stefan
 
R

Robert

Stefan said:
Robert, 01.02.2010 14:36:

I meant "parsed" in the sense of "has parsed and is now working on".



Sure, perfectly valid use case.



That's up to you. If you only apply local changes that do not change any
surrounding whitespace, you'll be fine.



HTML editors don't work that way. They always "re-spit-out" the whole code
when you click on "save". They certainly don't track the original file
position of tags. What they preserve is the content, including whitespace
(or not, if they reformat the code, but that's usually an *option*).



Sorry, but that's nonsense. The file position of a tag is determined by
whitespace, i.e. line endings and indentation. lxml does not alter that,
unless you tell it do do so.

Since you keep claiming that it *does* alter it, please come up with a
reproducible example that shows a) what you do in your code, b) what your
input is and c) what unexpected output it creates. Do not forget to include
the version number of lxml and libxml2 that you are using, as well as a
comment on /how/ the output differs from what you expected.

My stab in the dark is that you forgot to copy the tail text of elements
that you replace by new content, and that you didn't properly indent new
content that you added. But that's just that, a stab in the dark. You
didn't provide enough information for even an educated guess.

I think you confused the logical level of what I meant with "file
position":
Of course its not about (necessarily) writing back to the same
open file (OS-level), but regarding the whole serializiation
string (wherever it is finally written to - I typically write the
auto-converted HTML files to a 2nd test folder first, and want use
"diff -u ..." to see human-readable what changed happened - which
again is only reasonable if the original layout is preserved as
good as possible )

lxml and BeautifulSoup e.g. : load&parse a HTML file to a tree,
immediately serialize the tree without changes => you see big
differences of original and serialized files with quite any file.

The main issue: those libs seem to not track any info about the
original string/file positions of the objects they parse. The just
forget the past. Thus they cannot by principle do what I want it
seems ...

Or does anybody see attributes of the tree objects - which I
overlooked? Or a lib which can do or at least enable better this
source-back-connected editing?


Robert
 
T

Tim Arnold

I think I understand what you want, but I don't understand why yet. Do you
want to view the differences in an IDE or something like that? If so, why
not pretty-print both and compare that?
--Tim
 
N

Nobody

I tried lxml, but after walking and making changes in the element
tree, I'm forced to do a full serialization of the whole document
(etree.tostring(tree)) - which destroys the "human edited" format
of the original HTML code.
makes it rather unreadable.

is there an existing HTML parser which supports tracking/writing
back particular changes in a cautious way by just making local
changes? or a least tracks the tag start/end positions in the file?

HTMLParser, sgmllib.SGMLParser and htmllib.HTMLParser all allow you to
retrieve the literal text of a start tag (but not an end tag).
Unfortunately, they're only tokenisers, not parsers, so you'll need to
handle minimisation yourself.
 

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