| msg77108 - (view) |
Author: Lennart Regebro (lregebro) |
Date: 2008-12-06 09:55 |
| The whatsnew/3.0.rst document claims "It is not recommended to try to write source code that runs unchanged under both Python 2.6 and 3.0; you’d have to use a very contorted coding style, e.g. avoiding print statements, metaclasses, and much more. " This is no longer true, since 2.6 now has much backwards compatibility, including fopr print statements and unicode, so it's prefectly possible and not at all contorted to support both any longer. I'd recommend that the above statement is changed to "under both Python 2.5 and 3.0" or simply removed. |
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| msg77109 - (view) |
Author: Raymond Hettinger (rhettinger) *  |
Date: 2008-12-06 10:02 |
| No thanks. We need to STRONGLY discourage such efforts. The official recommended approach is to run 2.6 with a -3 option to identify code that cannot be automatically converted and then after making the appropriate updates to use the 2-to-3 converter. Trying to bypass that path is asking for unnecessary pain. |
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| msg77110 - (view) |
Author: Lennart Regebro (lregebro) |
Date: 2008-12-06 10:05 |
| That is not true, and statement as it stands now is still factually incorrect. |
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| msg77111 - (view) |
Author: Raymond Hettinger (rhettinger) * |
Date: 2008-12-06 10:11 |
| Guido, the OP wants you to change your long-standing guidance on the relationship between 2.6 and 3.0. Care to pronounce? |
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| msg77157 - (view) |
Author: Guido van Rossum (gvanrossum) * |
Date: 2008-12-06 18:25 |
| It is true for 2.6 unless you use various from __future__ imports, which I consider a form of contortion. Even with 2.6 I don't see how you can specify a metaclass without doing something weird like foo = MyMetaclass('foo', bases_tuple, namespace_dict) which is hardly an improvement over either the 2.x or 3.0 syntax. Given that it will always be true for 2.5, I don't want to back down. |
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| msg77161 - (view) |
Author: Lennart Regebro (lregebro) |
Date: 2008-12-06 18:59 |
| A future import is not much of a contortion, and metaclasses is not exactly an everyday occurrence, after 9 years of python I have yet to write a metaclass... Of course I don't like that it specifically mentiones 2.6, while 2.6 has lot's of forwards compatibility just to make it possible to write code that runs under both. It will always be true for 2.5, and then we could fix the issue by changing 2.6 to 2.5. If you want to keep the statement for 2.6, it could possibly be reformulated less strongly, or as a minimum change come up with another example than something that actually has a forward compatibility in 2.6. |
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| msg77163 - (view) |
Author: Guido van Rossum (gvanrossum) * |
Date: 2008-12-06 19:07 |
| You're misrepresenting or misunderstanding the goal of 2.6. Its goal isn't to make it easy to write code that runs under both. Its stated goal is to make it easy to write code that can easily be *ported* to 3.0. That's a very different story. I will not be taking it back. If you want further discussion on this, open a thread on python-dev. |
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| msg77164 - (view) |
Author: Lennart Regebro (lregebro) |
Date: 2008-12-06 19:10 |
| I've never said that is the goal. You are misrepresenting or misinterpreting my standpoint. |
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| msg77165 - (view) |
Author: Guido van Rossum (gvanrossum) * |
Date: 2008-12-06 19:14 |
| Then what did you mean by "just to make it possible to write code that runs under both" ? |
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| msg77166 - (view) |
Author: Lennart Regebro (lregebro) |
Date: 2008-12-06 19:18 |
| Well, that *is* the intention of a from __future__ import, isn't it? That doesn't mean that's the intention of 2.6 as a whole, just that statement. |
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| msg77167 - (view) |
Author: Guido van Rossum (gvanrossum) * |
Date: 2008-12-06 20:15 |
| But that's all part of the "make it easy to port" strategy. I stick to my claim that trying to write code that runs unchanged in 3.0 is a non-goal of Python 2.6, and I do not want to suggest that this is a good idea in the official documentation. |
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| msg77214 - (view) |
Author: Lennart Regebro (lregebro) |
Date: 2008-12-07 05:02 |
| Fair enough, but I still think we can come up with a better example that requires more contortions than "print", which doesn't. I think a good example of contortions is binary file data, which has two different types in 2.6 and 3.0. Also making sure that you use iterators all the time when using large sets of data can get quite contorted. |
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