twisted.web.template: unable to use a dynamic renderer to omit an attribute
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Description
 |
@glyph reported |
|---|---|
| Trac ID | trac#5213 |
| Type | enhancement |
| Created | 2011-07-30 19:51:03Z |
Trying to write some HTML generation code that doesn't manipulate tags (so that precompilation can one day make it fast) I needed to conditionally render an attribute: specifically, the selected attribute of an option tag. If selected appears at all, regardless of its value, browsers will treat that option as the active one. I thought that this example would remove the class attribute from a div:
#!py
import sys
from twisted.web.template import (
Element, XMLString, renderer, flattenString)
class ConditionalAttr(Element):
loader = XMLString(
"""
<html xmlns:t="http://twistedmatrix.com/ns/twisted.web.template/0.1">
<div><t:attr t:render="maybe" name="class">hello</t:attr></div>
</html>
""")
@renderer
def maybe(self, request, tag):
return ""
flattenString(None, ConditionalAttr()).addCallback(sys.stdout.write)
but as you can see if you run it, it simply renders an empty 'class' unconditionally. This seems odd, as the renderer is on the t:attr itself, and any other node rendered thusly would be removed from the DOM entirely.
Searchable metadata
trac-id__5213 5213
type__enhancement enhancement
reporter__glyph glyph
priority__normal normal
milestone__
branch__
branch_author__
status__new new
resolution__None None
component__web web
keywords__
time__1312055463000000 1312055463000000
changetime__1374526902000000 1374526902000000
version__None None
owner__
cc__jknight cc__indigo cc__glyph
Contributor guide
First steps
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- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the reproduced example in twisted.web.template, particularly the Element, XMLString, renderer, and flattenString entry points, and trace how a t:attr renderer result is handled. Confirm the current output and determine how an empty renderer result should affect the class or selected attribute; the issue names no specific source file or test, so the relevant coverage must be located.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- web-dev
- Issue type
- Feature
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100