[Python-Dev] PEP 343 - Abstract Block Redux

[Nick Coghlan]

Guido van Rossum wrote:
> I've written up the specs for my "PEP 340 redux" proposal as a
> separate PEP, PEP 343.
> 
> http://python.org/peps/pep-0343.html
> 
> Those who have been following the thread "Merging PEP 310 and PEP
> 340-redux?" will recognize my proposal in that thread, which received
> mostly positive responses there.
> 
> Please review and ask for clarifications of anything that's unclear.

+1 here.

The stdout redirection example needs to be corrected to avoid yielding inside a 
try/finally though:

     5. Redirect stdout temporarily:

         @do_template
         def redirecting_stdout(new_stdout):
             save_stdout = sys.stdout
             try:
                 sys.stdout = new_stdout
             except:
                 sys.stdout = save_stdout
                 raise
             else:
                 yield None
                 sys.stdout = save_stdout

        Used as follows:

         do opening(filename, "w") as f:
             do redirecting_stdout(f):
                 print "Hello world"

This could be left as the more elegant original if iterator finalisation (e.g. 
using a "__finish__()" slot) came in at the same time as user defined 
statements, allowing the above to be written naturally with try/finally.

Arnold deVos's HTML tagging example would need access to the exception 
information and could be rewritten as a class:

   def tag(object):
       def __init__(self, name):
           self.name = cgi.escape(name)

       def __enter__(self):
           print '<%s>' % self.name
           return self.name

       def __exit__(self, *exc_info):
           if not exc_info or exc_info[0] is None:
               print '</%s>' % self.name

Used as follows::

   do tag('html'):
       do tag('head'):
          do tag('title'):
             print 'A web page'
       do tag('body'):
          for par in pars:
             do tag('p'):
                print par

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
---------------------------------------------------------------
             http://boredomandlaziness.blogspot.com