Moving from Python 2 to Python 3: A 4 page "cheat sheet"
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From: Terry Reedy on 1 Dec 2009 16:55 Mark Summerfield wrote: > I've produced a 4 page document that provides a very concise summary > of Python 2<->3 differences plus the most commonly used new Python 3 > features. It is aimed at existing Python 2 programmers who want to > start writing Python 3 programs and want to use Python 3 idioms rather > than those from Python 2 where the idioms differ. > > It uses Python 3.1 syntax since that looks like being the standard for > a few years in view of the language moratorium. > > The document is U.S. Letter size but will also print fine on A4 > printers. > > It is available as a free PDF download (no registration or anything) > from InformIT's website. Here's the direct link: > http://ptgmedia.pearsoncmg.com/imprint_downloads/informit/promotions/python/python2python3.pdf > > And of course, if you want more on Python 3, there's always the > documentation---or my book:-) > "Programming in Python 3 (Second Edition)" ISBN-10: 0321680561. What might be even *more* helpful, with contributions from others perhaps, would be an indication of which changes are handled automatically by 2to3.py and which must be done by hand. tjr
From: John Bokma on 1 Dec 2009 18:52 Mark Summerfield <list(a)qtrac.plus.com> writes: > It is available as a free PDF download (no registration or anything) > from InformIT's website. Here's the direct link: > http://ptgmedia.pearsoncmg.com/imprint_downloads/informit/promotions/python/python2python3.pdf Thanks! > And of course, if you want more on Python 3, there's always the > documentation---or my book:-) > "Programming in Python 3 (Second Edition)" ISBN-10: 0321680561. Meh, second edition already? Haven't read the entire first edition yet. Which is IMO a good book (I also gave it to my brother as a present). Only negative point (to me) so far is that in the beginning (p8-9) the book mentions placing Python programs in C:\py3eg which gives me the unpleasant feeling that someone is coding on Windows XP with Administrator rights... Anyway, will add the 2nd edition to my wish list and donate the current one to the library in Xalapa (USBI) if they want it :-) John
From: Mark Summerfield on 2 Dec 2009 03:01 On 1 Dec, 17:50, Mark Dickinson <dicki...(a)gmail.com> wrote: > On Dec 1, 2:03 pm, Mark Summerfield <l...(a)qtrac.plus.com> wrote: > > > I've produced a 4 page document that provides a very concise summary > > of Python 2<->3 differences plus the most commonly used new Python 3 > > features. > > Very nice indeed! > > My only quibble is with the statement on the first page that > the 'String % operator is deprecated'. I'm not sure that's > true, for all values of 'deprecated'. There don't appear > to be any definite plans for getting rid of it just yet. > > Mark I didn't make this up:-) According to http://docs.python.org/dev/3.0/whatsnew/3.0.html "The plan is to eventually make this the only API for string formatting, and to start deprecating the % operator in Python 3.1."
From: Mark Summerfield on 2 Dec 2009 03:10 On 1 Dec, 18:30, Lie Ryan <lie.1...(a)gmail.com> wrote: > On 12/2/2009 1:03 AM, Mark Summerfield wrote: > > > > > I've produced a 4 page document that provides a very concise summary > > of Python 2<->3 differences plus the most commonly used new Python 3 > > features. It is aimed at existing Python 2 programmers who want to > > start writing Python 3 programs and want to use Python 3 idioms rather > > than those from Python 2 where the idioms differ. > > > It uses Python 3.1 syntax since that looks like being the standard for > > a few years in view of the language moratorium. > > > The document is U.S. Letter size but will also print fine on A4 > > printers. > > > It is available as a free PDF download (no registration or anything) > > from InformIT's website. Here's the direct link: > >http://ptgmedia.pearsoncmg.com/imprint_downloads/informit/promotions/... > > > And of course, if you want more on Python 3, there's always the > > documentation---or my book:-) > > "Programming in Python 3 (Second Edition)" ISBN-10: 0321680561. > > Nice. Thanks! > I suggest changing the lambda example a bit, the current example says: > Python 2 Python 3 > lambda (a,b): a + b lambda t: t[0] + t[1] > lambda a, b: a + b > > into something like: > > Python 2 Python 3 > lambda (a,b),c: a + b + c lambda t, c: t[0] + t[1] + c > lambda a, b, c: a + b + c > > it is unclear at first sight that it refers to tuple argument unpacking. Your proposed example is clearer in some respects, but mine is more minimal. And I think that anyone who _thinks_ about mine will get the point. (The document is short, but I never claimed it was a quick read;-) > There should also some mention that tuple argument unpacking for regular > function (def) is also gone. I probably should have, but it is hard to fit any more in... esp. since I don't want to take anything out. > Also, I'm not sure what this change is referring to: > Python 2 Python 3 > L = list(seq) L = sorted(seq) > L.sort() > > L.sort is still available in python, and sorted() have been available > since python 2. Both list.sort() and sorted() are for different purpose, > and neither will be deprecated. What's the change here? The document is about idioms as well as changes. In this case both approaches work in both versions, but it seems that there are still a lot of people who don't know about sorted(), so I put it in to show it as an idiom.
From: Mark Summerfield on 2 Dec 2009 03:13
On 1 Dec, 21:55, Terry Reedy <tjre...(a)udel.edu> wrote: > Mark Summerfield wrote: > > I've produced a 4 page document that provides a very concise summary > > of Python 2<->3 differences plus the most commonly used new Python 3 > > features. It is aimed at existing Python 2 programmers who want to > > start writing Python 3 programs and want to use Python 3 idioms rather > > than those from Python 2 where the idioms differ. > > > It uses Python 3.1 syntax since that looks like being the standard for > > a few years in view of the language moratorium. > > > The document is U.S. Letter size but will also print fine on A4 > > printers. > > > It is available as a free PDF download (no registration or anything) > > from InformIT's website. Here's the direct link: > >http://ptgmedia.pearsoncmg.com/imprint_downloads/informit/promotions/... > > > And of course, if you want more on Python 3, there's always the > > documentation---or my book:-) > > "Programming in Python 3 (Second Edition)" ISBN-10: 0321680561. > > What might be even *more* helpful, with contributions from others > perhaps, would be an indication of which changes are handled > automatically by 2to3.py and which must be done by hand. > > tjr No, that's exactly what I did not want to cover and the document says so up front. It is aimed at people who want Python 3 to come from their own brains and fingers! Also, the kind of info you're talking about is covered elsewhere, for example: http://diveintopython3.org/porting-code-to-python-3-with-2to3.html |