[Python-Dev] PEP 343 - next steps

[Nick Coghlan]

Guido van Rossum wrote:
> We considered this at some point during the PEP 340/343/346 discussion
> (in fact I had it this way in an early version of one of the PEPs),
> and in the end decided against it. I believe the argument was that any
> failure *before* __enter__() returns can be handled by try/except
> clauses inside __init__() or __enter__().

Hmm, you're right. Also, given implementation of PEP 343, code which 
genuinely has to care about this can do so manually:

   with async_exceptions_blocked():
       with critical_resource():
           with async_exceptions_unblocked():
               # Do the real work

This ensures acquisition of the critical resource is not interrupted. 
Even better, the above can be wrapped up in a template and still give 
the desired guarantees:

   @stmt_template
   def safe_acquisition(resource):
       with async_exceptions_blocked():
           with resource():
               with async_exceptions_unblocked():
                   yield None


   with safe_acquisition(critical_resource):
       # Do the real work

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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