[Python-ideas] Possible PEP 380 tweak (original) (raw)

Guido van Rossum guido at python.org
Sat Oct 30 05:11:24 CEST 2010

On Mon, Oct 25, 2010 at 6:35 PM, Jacob Holm <jh at improva.dk> wrote:

I had some later suggestions for how to change the expansion, see e.g. http://mail.python.org/pipermail/python-ideas/2009-April/004195.html  (I find that version easier to reason about even now 1½ years later)

I like that style too. Here it is with some annotations.

 _i = iter(EXPR)
 _m, _a = next, (_i,)
 # _m is a function or a bound method;
 #  _a is a tuple of arguments to call _m with;
 # both are set to other values further down
 while 1:
     # Move the generator along
     try:
         _y = _m(*_a)
     except StopIteration as _e:
         _r = _e.value
         break

     # Yield _y and process what came back in
     try:
         _s = yield _y
     except GeneratorExit as _e:
         # Request to exit
         try:
             # NOTE: This _m is unrelated to the other
             _m = _i.close
         except AttributeError:
             pass
         else:
             _m()
         raise _e  # Always exit
     except BaseException as _e:
         # An exception was thrown in; pass it along
         _a = sys.exc_info()
         try:
             _m = _i.throw
         except AttributeError:
             # Can't throw it in; throw it back out
             raise _e
     else:
         # A value was sent in; pass it along
         if _s is None:
             _m, _a = next, (_i,)
         else:
             _m, _a = _i.send, (_s,)

 RESULT = _r

I do note that this is a bit subtle; I don't like the reusing of _m and it's hard to verify that _m and _a are set on every path that goes back to the top of the loop.

-- --Guido van Rossum (python.org/~guido)

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