[Python-bugs-list] [ python-Bugs-495978 ] It's the future for generators

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Bugs item #495978, was opened at 2001-12-21 17:17
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Category: Python Interpreter Core
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Tim Peters (tim_one)
Assigned to: Nobody/Anonymous (nobody)
Summary: It's the future for generators

Initial Comment:
"from __future__ import generators" should no longer 
be required in 2.3a1.  Such stmts should also be 
removed from the Python library (there's a script 
under Tools to automate this).

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>Comment By: Raymond Hettinger (rhettinger)
Date: 2002-06-20 02:59

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Can this be closed?
The library is free of from __future__ generators and the 
core doesn't require it now.

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Comment By: Guido van Rossum (gvanrossum)
Date: 2002-03-22 17:18

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It's not too late!  Neil hasn't checked it in yet.

Neil, would you be willing to change your patch so that it
disables the yield keyword using #ifdef rather than by
erasing all of the code?

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Comment By: Tim Peters (tim_one)
Date: 2002-03-22 16:59

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Na, you should read me as saying I don't know how to write 
the kinds of docs you want.  I didn't do the parser changes 
here, so if you think there's something predictable and 
useful to be said here, you're the one to say it.

Keeping at least one example around under an "#if 0" sounds 
like an excellent idea.  The last time I implemented a 
future gimmick, it was spread around in so many places that 
the only sane way to proceed was to search for "the other" 
future gimmick that happened to be implemented already.

But doing that kind of search again is the only sane way I 
know to get rid of the future-generator business now too.

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Comment By: Guido van Rossum (gvanrossum)
Date: 2002-03-22 16:39

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Actually, each time a future feature introduces a new
keyword that has to remain an identifier when the feature is
not enabled, almost *exactly* the same hacks have to be
applied to the parser. That's just how the parser works. I
would almost recommend keeping those changes around at all
times, just #ifdef'ed out or something.

The other stuff that feels like it's very similar each time
is the handling of the flags passed around between the
various passes of the code generator.

But I know it's hopeless to argue with you, so I'll let you
rediscover all that when you decide to finally implement the
braces feature. :-)

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Comment By: Tim Peters (tim_one)
Date: 2002-03-22 16:22

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The internal future machinery has changed every time we've 
added a new future gimmick.  So there's really nothing to 
be said other than to scour the source code looking for now-
obsolete "stuff".  For example, it's possible that the 
kinds of parser changes made for "yield" will never happen 
again, and, even if they do, I think it's impossible to 
predict where and how the parser will need to be unchanged.

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Comment By: Guido van Rossum (gvanrossum)
Date: 2002-03-22 16:13

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There ought to be documentation on what to do when an
optional feature becomes mandatory. Maybe a block comment or
docstring in __future__.py?


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Comment By: Tim Peters (tim_one)
Date: 2002-03-22 15:34

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Neil, if you don't enjoy using the patch system for 
straightforward stuff like this, don't feel compelled to 
use it.  That is, just check it in.

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Comment By: Neil Schemenauer (nascheme)
Date: 2002-03-22 15:04

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The attached patch removes the "yield is an optional keyword"
hacks from the parser.  It's not a complete fix for this
bug though.

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