[ZPT] Better Unicode support

[Andreas Jung]

Hi,

Zope 2 will hopefully use the Zope 3 ZPT implementation in the future.
Since the ZPT implementation will use unicode internally we have to deal
in some way with non-unicode in Zope 2 installations. We currently can not 
require that every callable object return unicode. Mixing unicode ZPTs with
non-unicode content will definitely lead to UnicodeDecodeErrors. I have 
some ideas I would like to discuss (especially how they fit into the 
current Zope 3  implemenation).

- better handling of UnicodeDecodeError: these errors will basically show up
  using tal:content and tal:replace. Path expressions or Python expression
  returning non-unicode content will be implicitly converted to Unicode
  possibly raising UnicodeDecodeErrors. Is there any chance in improving the
  error handling? means..trapping the error and presenting an error message
  showing the path expression or python expression causing the failure?


- implicit conversion of non-unicode content to unicode. In case of a path
  expression "context/someobject/method" either the method could provide a
  function attribute (method.output_encoding or so) specifiy the encoding
  of the result. If we would default to some reasonable encoding. We could
  also check for someobject.output_encoding as fallback. Dealing with python
  expressions like "python: context.someobject.method()" seems to be more
  complex because it likely requires somekind of parser to get hold of the
  'method' or 'someobject' (I am not sure if there is already some code
  in TAL for this).

I've never had a closer look at the TAL code to be able to make a decision 
if these issues can be resolved in a sane way. Any comments?



-aj








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