[ZPT] Semantics of double slash in path expressions changed from Zope2.5.1 to 2.6?

[Dieter Maurer]

Clemens Robbenhaar writes:
 > ....
 >  After reading the diff of the sources I found there is an explanation
 > for this change as a fix for http://collector.zope.org/Zope/581
 > 
 >  The issue has been that one cannot do things like 'd/?k' in 2.5.1,
 > when "k" evaluates to the empty string. As 'd' may be something with
 > item access, this may make indeed sense, as the empty string is not a
 > valid id, but a valid key for an item.
 > 
 > E.g.: 
 > 
 >  <tal:block 
 >     define="
 >        d python:{'1':'Yabba', '0':'Yabba', '':'Hey!'}; 
 >        k string:"
 >     replace="d/?k">test</tal:block>
 >  
 >  renders "Hey!" with 2.6.0, but creates an error with 2.5.1
 > 
 > Now as some 'd.maurer' has collected this issue, who is most probably
 > Dieter Maurer,
Indeed.
 > I guess there are real use cases for this issue. ;)
Sure.

  A real life example caused the exception that led me
  to file the bug report.


 >  But are there uses cases for empty string access without the '/?'
 > notation?
Sure. The same as with the "?variable" syntax:

Path expressions are supposed to access dictionaries (with strings
as keys). Suppose, one of its keys it the empty string.
How will you access it via a path expression?

It would not be senseful to treat

   tal:define="XXX	 string:something;
	       ...       .../?XXX/...;
	      "

different from

   tal:define="...	.../something/...;"

 > ....
 >  A possible workaround would be to treat double slashes as a single one
 > when splitting a path expression. This would leave the solution for
 > the collector issue #581 intact but avoid the less intuitive behaviour
 > for multiple consecutive slashes. 
It would no address the "empty key" issue for dictionaries.



Dieter