Why is the migration to py3k a concern? For example I have libraries which use string%dictionary substitution where the dictionary is actually an object which emulates a dictionary. The __getitem__ for the object can be very expensive and is only called when needed by the string substitution.
In py3k string%dictionary is going away. Why? I have no idea.
The replacement is a string.format(...) method which supports dictionary calling. string.format(**dictionary) But dictionary calling doesn't support dictionary emulation. So in the example below the substitution works but the call fails.
=== code
class fdict(dict): def __getitem__(self, item): return "got("+item+")"
def fn(**d): print d["boogie"]
if __name__=="__main__": fd = fdict() print "attempting string substitution with fake dictionary" print print "hello there %(boogie)s" % fd # <-- works print print "now attempting function call with fake dictionary" print fn(**fd) # <-- fails
=== output
% python2.6 dtest.py attempting string substitution with fake dictionary
hello there got(boogie)
now attempting function call with fake dictionary
Traceback (most recent call last): File "dtest.py", line 17, in <module> fn(**fd) File "dtest.py", line 7, in fn print d["boogie"] KeyError: 'boogie'
==== end of output
Consequently there is no simple way to translate my code, I think. I suspect you will find this kind of subtle issue in many places. Or worse, you won't find it until after your program has been installed in production.
It's a damn shame because if string%dict was just left in it wouldn't be an issue.
Also, if making f(**d) support dict emulation has any negative performance implications then I don't want it please.
On Fri, 2008-04-18 at 08:58 -0700, Aaron Watters wrote: > Why is the migration to py3k a concern? > For example I have libraries which use string%dictionary > substitution where the dictionary is actually an object > which emulates a dictionary. The __getitem__ for > the object can be very expensive and is only called when > needed by the string substitution.
> In py3k string%dictionary is going away. Why? > I have no idea.
> The replacement is a string.format(...) method > which supports dictionary calling. > string.format(**dictionary) > But dictionary > calling doesn't support dictionary emulation. > So in the example below the substitution works > but the call fails.
> === code
> class fdict(dict): > def __getitem__(self, item): > return "got("+item+")"
> def fn(**d): > print d["boogie"]
> if __name__=="__main__": > fd = fdict() > print "attempting string substitution with fake dictionary" > print > print "hello there %(boogie)s" % fd # <-- works > print > print "now attempting function call with fake dictionary" > print > fn(**fd) # <-- fails
> now attempting function call with fake dictionary
> Traceback (most recent call last): > File "dtest.py", line 17, in <module> > fn(**fd) > File "dtest.py", line 7, in fn > print d["boogie"] > KeyError: 'boogie'
> ==== end of output
> Consequently there is no simple way to translate > my code, I think. I suspect you will find this kind of subtle > issue in many places. Or worse, you won't find it > until after your program has been installed > in production.
> It's a damn shame because > if string%dict was just left in it wouldn't be an issue.
> Also, if making f(**d) support dict emulation > has any negative performance implications > then I don't want it please.
I was with you on this issue right up until that last paragraph. You want it, but only if its free. That's ridiculous. Every thing a computer does requires processor cycles.
Do you really mean to tell me that string interpolation has been a major bottleneck for you? Now I think you're just whining because you like to hear yourself whine. Try coming up with a real standard for evaluation. How much of a performance hit will actually cause you trouble? 1% extra on string interpolation? 10%? 50%? 200%?
You do provide a link to a website called xfeedme.com. And I just fed you. IHBT. HAND. :-/
-- Oook, J. Cliff Dyer Carolina Digital Library and Archives UNC Chapel Hill
> Try coming up with a real standard for evaluation. > How much of a performance hit will actually cause you trouble? 1% extra > on string interpolation? 10%? 50%? 200%?
You misread my comment. I don't want function calls to support dictionary emulation if there is a speed penalty because this is such a special case and function calls are so important. I don't really know, but I think "fixing" the above issue for string.format(...) might involve changing the representation of every python stack frame... not worth it in this case if there is any penalty (afaik there isn't).
An alternative is to provide an alternate interface to string.format so that you could pass in an object which might emulate a dictionary, like string.formatDict(D) -- or you could even adopt a shortcut notation like string % D -- hey there's an idea! -- Aaron Watters
On 18 Apr., 20:07, Aaron Watters <aaron.watt...@gmail.com> wrote:
> I don't really know, but I think "fixing" the above issue for > string.format(...) might involve changing the representation of > every python stack frame... not worth it in this case if there > is any penalty (afaik there isn't).
In Python 2.6 the format function simply calls PyDict_GetItem on the dictionary object and raises a KeyError if it fails. A dict emulation would require one more lookup if the fast lookup has no result. It would be a speed penalty in the general case if this lookup would be implemented in PyDict_GetItem but handling a special case in the format implementation might not look that bad.
> Why is the migration to py3k a concern? > For example I have libraries which use string%dictionary > substitution where the dictionary is actually an object > which emulates a dictionary. The __getitem__ for > the object can be very expensive and is only called when > needed by the string substitution.
> In py3k string%dictionary is going away. Why? > I have no idea.
> The replacement is a string.format(...) method > which supports dictionary calling. > string.format(**dictionary) > But dictionary > calling doesn't support dictionary emulation. > So in the example below the substitution works > but the call fails.
> === code
> class fdict(dict): > def __getitem__(self, item): > return "got("+item+")"
> def fn(**d): > print d["boogie"]
> if __name__=="__main__": > fd = fdict() > print "attempting string substitution with fake dictionary" > print > print "hello there %(boogie)s" % fd # <-- works > print > print "now attempting function call with fake dictionary" > print > fn(**fd) # <-- fails
> now attempting function call with fake dictionary
> Traceback (most recent call last): > File "dtest.py", line 17, in <module> > fn(**fd) > File "dtest.py", line 7, in fn > print d["boogie"] > KeyError: 'boogie'
> ==== end of output
> Consequently there is no simple way to translate > my code, I think. I suspect you will find this kind of subtle > issue in many places. Or worse, you won't find it > until after your program has been installed > in production.
> It's a damn shame because > if string%dict was just left in it wouldn't be an issue.
> Also, if making f(**d) support dict emulation > has any negative performance implications > then I don't want it please.
The reason it doesn't work is that you are unpacking the dictionary with **, and you have done nothing to define any keys or define a length. I would describe the way you are using dict as a hack, and not part of any standard feature. You make a good point that it breaks your code, but at the same time the format facility gives you the ability to do something similar but in a standard way. You simply define a class with a __format__ method and pass that in instead of your dict.
class MyClass: def __format__(self, spec): return "got({0})".format(spec)
c = MyClass() print ("hey everybody {0:some words}".format(c)) print ("lets try this {0:more words} {0:even more words}".format(c))
should produce:
hey everybody got(some words) lets try this got(more words) got(even more words)
My point is that instead of exploiting the string formatting of dictionaries feature to create a custom format specifier, you actually get to define your own format specifiers, something which is much more powerful.
And actually, you can do this too... which is even simpler and allows you to use your a portion of your existing solution:
class fdict(dict): def __getitem__(self, item): return "got("+item+")"
fd = fdict() print ("hello there {0[boogie]} hello there {0[george])".format(fd))
Which should result in:
hello there got(boogie) hello there got(george)
* Keep in mind that I have not tested any of this code, there may be bugs. I don't have Py3k or 2.6 installed locally.
I think this is a good trade-off.
Adding to that... don't worry about py3k. Nobody is forcing you to switch. In fact, you are encouraged not to until you are comfortable. Py3k won't _break_ your code. You wrote the code for Python 2.x use it in 2.x. Python 2.x probably has a good 5-10 years remaining.
On 18 Apr., 23:09, Matimus <mccre...@gmail.com> wrote:
> The reason it doesn't work is that you are unpacking the dictionary > with **, and you have done nothing to define any keys or define a > length.
This is a non-issue. The class derives from dict; it has all the desired attributes. It is also not a problem in particular because these properties are not requested by format ( at least not in the code I have examined which was admittedly just a critical section that caused the exception ).
> Adding to that... don't worry about py3k. Nobody is forcing you to > switch. In fact, you are encouraged not to until you are comfortable. > Py3k won't _break_ your code. You wrote the code for Python 2.x use it > in 2.x. Python 2.x probably has a good 5-10 years remaining.
These advices start to get annoying.
Software hardly ever exists in isolation for the sake of the beauty of the algorithm but is supplementary to a large framework/engine/ library. So if e.g. Django switches to 3 everyone who works with it has to switch sooner or later as well or lose track otherwise, no matter how long Python 1.5.2 or Python 2.5.2 or whatever version will be maintained. If Pythons code base becomes fragmented it will be harmful and affect almost everyones work.
On Fri, 18 Apr 2008 16:19:38 -0700, Kay Schluehr wrote: > On 18 Apr., 23:09, Matimus <mccre...@gmail.com> wrote: >> The reason it doesn't work is that you are unpacking the dictionary >> with **, and you have done nothing to define any keys or define a >> length.
> This is a non-issue. The class derives from dict; it has all the desired > attributes. It is also not a problem in particular because these > properties are not requested by format ( at least not in the code I have > examined which was admittedly just a critical section that caused the > exception ).
>> Adding to that... don't worry about py3k. Nobody is forcing you to >> switch. In fact, you are encouraged not to until you are comfortable. >> Py3k won't _break_ your code. You wrote the code for Python 2.x use it >> in 2.x. Python 2.x probably has a good 5-10 years remaining.
> These advices start to get annoying.
> Software hardly ever exists in isolation for the sake of the beauty of > the algorithm but is supplementary to a large framework/engine/ library. > So if e.g. Django switches to 3 everyone who works with it has to switch > sooner or later as well or lose track otherwise, no matter how long > Python 1.5.2 or Python 2.5.2 or whatever version will be maintained. If > Pythons code base becomes fragmented it will be harmful and affect > almost everyones work.
This Py3k-Django-related FUD starts to get annoying. AFAIK Django is going to support everything from 2.3 to 3.0 from single codebase. 2to3 tool will be called from setup.py and code will have few 'if sys.version_info < (3, 0)/else' tricks. Proof of concept already exists: http://wiki.python.org/moin/PortingDjangoTo3k
I work with Django as well as *on* Django and 3rd party Django addons and don't see any reason to worry.
Your particular problem may be solved by using a real dictionary with real keys which will probably have positive performance impact on your code and make it more clean.
Even if Python code base will become fragmented why is it harmfull? This is a way our life work - you rise and get better or die. It is essential part of progress and evolution. IMHO, we'll only get better Python and better Python libraries.
> On 18 Apr., 23:09, Matimus <mccre...@gmail.com> wrote:
> > The reason it doesn't work is that you are unpacking the dictionary > > with **, and you have done nothing to define any keys or define a > > length.
> This is a non-issue. The class derives from dict; it has all the > desired attributes. It is also not a problem in particular because > these properties are not requested by format ( at least not in the > code I have examined which was admittedly just a critical section that > caused the exception ).
> > Adding to that... don't worry about py3k. Nobody is forcing you to > > switch. In fact, you are encouraged not to until you are comfortable. > > Py3k won't _break_ your code. You wrote the code for Python 2.x use it > > in 2.x. Python 2.x probably has a good 5-10 years remaining.
> These advices start to get annoying.
> Software hardly ever exists in isolation for the sake of the beauty of > the algorithm but is supplementary to a large framework/engine/ > library. So if e.g. Django switches to 3 everyone who works with it > has to switch sooner or later as well or lose track otherwise, no > matter how long Python 1.5.2 or Python 2.5.2 or whatever version will > be maintained. If Pythons code base becomes fragmented it will be > harmful and affect almost everyones work.
This has happened before, though -- I remember the pain of moving to 2.0 from the 1.5 branch way back when, and it wasn't getting my 1.5 code to work in 2.0, it was being jealous of all the cool features of 2.0 that I had to wait to get. I was working in production with 1.5 in 2000 and all the libraries available for Python gradually stopped supporting 1.5 to pick up interesting 2.0 features that actually made them easier to work with, and new libraries all began to assume you were using a 2.0+ Python version because that's what was current. By 2003-2004 everyone I knew had switched over to 2.0, but by then I had had nearly 5 years to port my legacy 1.5 code to 2.0, take advantage of the 2.0 version's features, and do plenty of testing of my 1.5 codebase in 2.0 before I switched my production systems over. Not to mention the fact that plenty of warning was offered BEFORE 2.0 was released and 1.5 was not abruptly ended, but gradually phased out until only the teeniest far ends of the long tail were using it. The 2.6->3.0 process is going to be even less of a pain than the 1.5->2.0 conversion, which was not hard at all going forward into it. You may not want to switch, but by the time you decide to it will be pretty easy to move on -- the extreme opposite reality being your application will be so frozen that both your Python version and your codebase will be fossils, left to hum on completely unchanged on some forgotten server like so much other legacy code.
> Why is the migration to py3k a concern? > For example I have libraries which use string%dictionary > substitution where the dictionary is actually an object > which emulates a dictionary. The __getitem__ for > the object can be very expensive and is only called when > needed by the string substitution.
> In py3k string%dictionary is going away. Why? > I have no idea.
> The replacement is a string.format(...) method > which supports dictionary calling. > string.format(**dictionary) > But dictionary > calling doesn't support dictionary emulation. > So in the example below the substitution works > but the call fails.
> === code
> class fdict(dict): > def __getitem__(self, item): > return "got("+item+")"
> def fn(**d): > print d["boogie"]
> if __name__=="__main__": > fd = fdict() > print "attempting string substitution with fake dictionary" > print > print "hello there %(boogie)s" % fd # <-- works > print > print "now attempting function call with fake dictionary" > print > fn(**fd) # <-- fails
> now attempting function call with fake dictionary
> Traceback (most recent call last): > File "dtest.py", line 17, in <module> > fn(**fd) > File "dtest.py", line 7, in fn > print d["boogie"] > KeyError: 'boogie'
> ==== end of output
> Consequently there is no simple way to translate > my code, I think. I suspect you will find this kind of subtle > issue in many places. Or worse, you won't find it > until after your program has been installed > in production.
> It's a damn shame because > if string%dict was just left in it wouldn't be an issue.
> Also, if making f(**d) support dict emulation > has any negative performance implications > then I don't want it please.
> sigh. -- Aaron Watters
If you don't like Python 3, DON'T USE IT.
It's been stated repeatedly that 2.x and 3.x are going to be supported in parallel for years.
Refusing to use 3, thus casting your brain-share vote against it, is far more likely to have an effect than you coming here and making everyone's life miserable with your pitiful whining.
> Why is the migration to py3k a concern? > For example I have libraries which use string%dictionary > substitution where the dictionary is actually an object > which emulates a dictionary. The __getitem__ for > the object can be very expensive and is only called when > needed by the string substitution.
> In py3k string%dictionary is going away. Why? > I have no idea.
But not soon. It's not listed in PEP 3100 and according to this message http://mail.python.org/pipermail/python-3000/2008-April/013094.html %s formatting will not disappear until Python 3.3 You have plenty of time to evaluate alternatives. Your code may become obsolete even before 3.3 is shipped.
On Apr 19, 4:42 am, Carl Banks <pavlovevide...@gmail.com> wrote:
> If you don't like Python 3, DON'T USE IT.
I've read this position a number of times in this and related threads, and it overlooks one constituency of Python developers - those who develop and support modules for use by other Python users. As the supporter of pyparsing, I really can't just "not use" Py3 - ignoring Py3 means shutting out/holding back those of my users who do want to use it, and pretty much consigning my module to eventual dustbin status. Ideally, I can implement some form of cross-compatible code so that I need maintain only a single code base, and I have managed to do so on a number of fronts (with the help of Robert A. Clark): - add support for both __bool__ and __nonzero__ (__nonzero__ calls __bool__, so that upgrading to Py3 actually saves a function call) - convert isinstance(x,basestring) to isinstance(x,__BASESTRING__) and dynamically set __BASESTRING__ to basestring or str - similar treatment for sys.maxint/maxsize -> __MAX_INT__
I dodged a bullet when 3.0a3 added back in support for the 2.x form of "except" for exception handling. 3.0a2 only supported "except varname as ExceptionType:" and there was no way I could do this in a multi- version compatible way.
My remaining hassle is print as function vs. print as statement. I provide a number of default diagnostic methods, and I have not fully gotten all to print nice - converting "print x" to "print (x)" is simple enough, and "print (x,y)" replaces "print x,y" well enough when running under Py3, but the same code in Py2.x now prints a tuple instead of a nice string like before. I will probably punt on the whole issue in the next release and just use sys.write.stdout/stderr throughout, and " ".join() the args (another function call!) before calling.
I wasn't aware of the coming deprecation of '%' string interpolation, but at least it is deferred until 3.3, which does give me a few years I should think before I absolutely must address it. This is really not so much an issue for me as it is for my "customers." Pyparsing returns its parsed tokens using a class that is dict-like in behavior, but without extending dict (duck-typing at its finest!). I really like that my users can parse an expression and access any named fields directly and neatly in an interpolated string using "%(field_name)s". If this is removed, pyparsing will continue to work as-is, but I feel like a nice ease-of-access mode will have been lost to those who use it.
Overall, I think I'm getting off pretty easy, but then pyparsing is a small module with very limited use of the standard lib. I can imagine that maintainers of larger libraries are having some serious fits trying to support both versions with a single code base. And as much as we all love Python-the-language, language features alone do not help a language and its community of users to grow and proliferate. I think most would agree that it is the cornucopia of libraries that really make Python an environment for developing production applications.
>I've read this position a number of times in this and related threads, >and it overlooks one constituency of Python developers - those who >develop and support modules for use by other Python users. As the >supporter of pyparsing, I really can't just "not use" Py3 - ignoring >Py3 means shutting out/holding back those of my users who do want to >use it, and pretty much consigning my module to eventual dustbin >status.
Eh. You can ingore it until your users start asking for it.
>Ideally, I can implement some form of cross-compatible code >so that I need maintain only a single code base, and I have managed to >do so on a number of fronts (with the help of Robert A. Clark): >- add support for both __bool__ and __nonzero__ (__nonzero__ calls >__bool__, so that upgrading to Py3 actually saves a function call)
Doing sometthing like the following would save the function call in both cases:
class C(object): def __bool__(self): return False
__nonzero__ = __bool__
>- convert isinstance(x,basestring) to isinstance(x,__BASESTRING__) and >dynamically set __BASESTRING__ to basestring or str >- similar treatment for sys.maxint/maxsize -> __MAX_INT__
I don't thiink using double underscores here is appropriate. It suggests it's part of the language. Since "basestring" is no longer part of the language, you could do:
if "basestring" not in globals(): basestring = str
>Overall, I think I'm getting off pretty easy, but then pyparsing is a >small module with very limited use of the standard lib.
Has the standard library changed that much? I thought was it mainly the deletion of old seldom used modules that happens in new releases anyways.
>[...] And as much as we all love Python-the-language, language features >alone do not help a language and its community of users to grow >and proliferate. I think most would agree that it is the cornucopia >of libraries that really make Python an environment for developing >production applications.
En Mon, 21 Apr 2008 16:42:41 -0300, Ross Ridge <rri...@caffeine.csclub.uwaterloo.ca> escribió:
>> Ideally, I can implement some form of cross-compatible code >> so that I need maintain only a single code base, and I have managed to >> do so on a number of fronts (with the help of Robert A. Clark):
Perhaps you can manage to keep your code compatible with all versions, but AFAIK the reccomended strategy is to write code compatible with Python 2.6 and use the 2to3 tool to generate the 3.0 source. And *not* edit the 3.0 code unless one wants to maintain two branches.
>> Overall, I think I'm getting off pretty easy, but then pyparsing is a >> small module with very limited use of the standard lib.
> Has the standard library changed that much? I thought was it mainly the > deletion of old seldom used modules that happens in new releases anyways.
*and* renaming of old module names that don't follow PEP8, and merging others into packages for better structure. That's another point where using the 2to3 tool is necesary -it takes care of such changes- unless one wants to maintain two branches.
> Why do you say that? It's not going away in Python 3.0.
I also got the impression that it was going away. PEP 3101's abstract says:
This PEP proposes a new system for built-in string formatting operations, intended as a replacement [sic] for the existing '%' string formatting operator.
Under "Backward compatibility" it says that both systems can coexist "until it comes time to deprecate the older system".
Gabriel Genellina wrote: >> Has the standard library changed that much? I thought was it mainly the >> deletion of old seldom used modules that happens in new releases anyways.
> *and* renaming of old module names that don't follow PEP8, and merging > others into packages for better structure. > That's another point where using the 2to3 tool is necesary -it takes > care of such changes- unless one wants to maintain two branches.
conditional imports were never a problem in Python. Once things are in their final place, you can add a try-except and import from two different places - unless (I assume) you want to use 2to3, which might even break this approach.
>>> In py3k string%dictionary is going away. >> Why do you say that? It's not going away in Python 3.0.
> I also got the impression that it was going away. PEP 3101's abstract > says:
> This PEP proposes a new system for built-in string formatting > operations, intended as a replacement [sic] for the existing '%' > string formatting operator.
> Under "Backward compatibility" it says that both systems can coexist > "until it comes time to deprecate the older system".
The PEP may say that it's going away, but it doesn't say that it goes away in 3.0 - and indeed, it won't.
At some point in the future, somebody will likely propose that the PEP will be executed. At that time, huge flame wars will start. I expect that they settle in changing the PEP to explain that the old mechanism gets removed in Python 4, to be release in 2018 :-)
>>>> In py3k string%dictionary is going away. >>> Why do you say that? It's not going away in Python 3.0.
>> I also got the impression that it was going away. PEP 3101's abstract >> says:
>> This PEP proposes a new system for built-in string formatting >> operations, intended as a replacement [sic] for the existing '%' >> string formatting operator.
>> Under "Backward compatibility" it says that both systems can coexist >> "until it comes time to deprecate the older system".
> The PEP may say that it's going away, but it doesn't say that it > goes away in 3.0 - and indeed, it won't.
Thanks for clarifying it. It is certainly unclear from the wording of the PEP, given that 3.0 is regarded as the Python version allowed to break backward compatibility.
> At some point in the future, somebody will likely propose that the > PEP will be executed. At that time, huge flame wars will start. I > expect that they settle in changing the PEP to explain that the old > mechanism gets removed in Python 4, to be release in 2018 :-)
On Apr 21, 9:01 pm, "Gabriel Genellina" <gagsl-...@yahoo.com.ar> wrote:
> Perhaps you can manage to keep your code compatible with all versions, but > AFAIK the reccomended strategy is to write code compatible with Python 2.6 > and use the 2to3 tool to generate the 3.0 source. And *not* edit the 3.0 > code unless one wants to maintain two branches.
Gabriel -
(Thanks for chiming in on this sub-thread, I really enjoy reading your posts.)
My point is that the recommended strategy MAY work for those who write end point applications (I consider maintaining 2 branches to be in the "not working" category), but it does NOT WORK for people who maintain modules for other people to use, because those people may be on a range of Python versions that extend beyond 2.6-3.0. So if I upgrade my module to 2.6, those running on earlier versions can no longer use it. At some point in the future, I'll probably be able to say "no more support for pre-2.6", but it is a bit early to start saying that now.
Likewise, I don't want to say "no support for 3.0" - people DO want to try 3.0 out, and I WANT them to want and be able to use my module too.
Given the recommended strategy, and ruling out dual codebase, whom do I tell that they can't use the next version of my module?
Again, to me, this is a non-issue because I've been able to create a cross-version compatible single codebase for pyparsing. But it was a bit dicey there for a while, and I think other module developers/ maintainers may not be so lucky.
So, I feel that the recommended strategy was devised with a narrow group of developers in mind, and leaves module developers/maintainers, who wish to target as broad a set of users as possible, faced with choosing one of these strategies: - create (if possible) single cross-version compatible code - forego support of 3.0 users - discontinue pre-2.6 support for future versions of their module - maintain dual codebase
> Again, to me, this is a non-issue because I've been able to create a > cross-version compatible single codebase for pyparsing. But it was a > bit dicey there for a while, and I think other module developers/ > maintainers may not be so lucky.
I'm more optimistic. I tried it for Django, and while the port is not complete, it goes really well and supports "basic" operations (i.e. the Django tutorial).
Based on your experience, and other reports, I think there is a fair chance that you can support a wide range of versions (2.x and 3.x) from a single code base for most projects.
> - create (if possible) single cross-version compatible code > - forego support of 3.0 users > - discontinue pre-2.6 support for future versions of their module > - maintain dual codebase
One needs to consider the drawbacks in each case; for the single codebase approach, the drawback probably is that readability suffers, and the need for testing increases (but it does always if you support multiple targets). It also requires expertise to create such cross-version code in the first place, but that's "just" a learning issue (i.e. you have to keep the rules in mind that you want to follow).
On Apr 24, 10:10 am, Paul McGuire <pt...@austin.rr.com> wrote
> end point applications (I consider maintaining 2 branches to be in the > "not working" category), but it does NOT WORK for people who maintain > modules for other people to use, because those people may be on a > range of Python versions that extend beyond 2.6-3.0. So if I upgrade > my module to 2.6, those running on earlier versions can no longer use > it. At some point in the future, I'll probably be able to say "no > more support for pre-2.6", but it is a bit early to start saying that > now.
In my view using a conversion tool on an ongoing basis is not an option. It just adds a dependancy. What happens when the conversion tool is upgraded in a non-backwards-compatible way? Or do we have assurance that it won't be ;)?
Will changes to the converter mean that the users of my converted libraries have to start using my tools in a different way? Even if it breaks some users in a very subtle way it's not acceptible. I have no interest in adding additional dependancies, with an additional degree of freedom to break.
This is all made worse because it's binary -- with upgrades to C or C# you usually had the option of cross linking between old style components and new style components (and at least with C these could usually be made to work) and you could port the older stuff with care. With py 3.0 and python 2.6 *everything* either works with the interpreter or none of it does. (Don't ask my users to install two interpreters: they'll just give up and use something else.)
So if I want to support both I have to do everything twice in the expected case and in the best case test everything twice, at the same time, if I want to support both versions and keep features in sync. This is of course assuming that all the supporting libraries do the same thing. If they don't and one of the libraries doesn't support 2.* and another doesn't support 3.*... I guess I'm just screwed.
I still think it's a shame, and I think it's different in kind from python 1.x->2.x. 2.x broke very little as I recall. Most 1.x code just worked in 2.x and most of the rest required very minor change. I think this is not the case for 2.x->3.x.
-- Aaron (Scummy) Watters, hoping to shut up now.
ps: I didn't notice that % was vanishing later (3.3). that's a bit better (whew ;) ).
pps: I have to note that it would be nice if the ad-hominem (sp?) invective would drop out of these threads -- it doesn't add a lot, I think.
The reason that successive versions of 2.x broke so little is that starting at about 2.2, all breakages (starting with int division change) were put off until until 3.0 instead of being implemented as decided upon (with warning, deprecation, and then removal). Now the debt comes due.
The new policy of mass breakage was a result of complaint about the old policy of gradual breakage. Of course, the new policy will get complaints both from those who preferred the old policy and those who want Python frozen with nothing ever removed for improvements. No change, gradual change, and jump change all have problems.
In a year, we will have a better idea of which was better.
> In my view using a conversion tool on an ongoing basis is > not an option. It just adds a dependancy. What happens when > the conversion tool is upgraded in a non-backwards-compatible > way? Or do we have assurance that it won't be ;)?
The latter: if you include a copy of the converter with your package, it won't change unless you change it. If you rely on the copy of the converter that ships with Python 3.0, you have the assurance that it won't change in a non-backwards-compatible manner in all of 3.0.y.
Of course, the copies include in later 3.x releases may change, but you'll have to test for the later 3.x releases, anyway, as they may show incompatible changes themselves.
> Will changes to the converter > mean that the users of my > converted libraries have to start > using my tools in a different way?
No. If the 2to3 converter is changed to support additional source patterns to convert, it either won't affect your code (if you don't use the pattern), or it may convert some of your code that it didn't previously - then that conversion may or may not be correct. So as a consequence, your library may stop working; then you'll have to adjust either your library, or go back to an older version of the converter.
In no case, however, will the users of the library need to adjust their code to changing 2to3 output. 2to3 won't change the library API.
> I have no interest in adding additional dependancies, > with an additional degree of freedom to break.
Then remove the freedom by fixing a specific 2to3 version (e.g. by including it).
> So if I want to support both I have to do everything > twice in the expected case and in the best case test > everything twice, at the same time, if I want to > support both versions and keep features in sync.
This I don't understand. Why do you think you have to do everything twice?
> I still think it's a shame [...] > pps: I have to note that it would be nice if the > ad-hominem (sp?) invective would drop out of > these threads -- it doesn't add a lot, I think.
shame 1 a. a painful emotion caused by consciousness of guilt, shortcoming, or impropriety 2 a condition of humiliating disgrace or disrepute
So who do you think should feel guilt? Or should be disgraced or disreputed?
>> Perhaps you can manage to keep your code compatible with all versions, >> but >> AFAIK the reccomended strategy is to write code compatible with Python >> 2.6 >> and use the 2to3 tool to generate the 3.0 source. And *not* edit the >> 3.0 >> code unless one wants to maintain two branches.
> Gabriel -
> (Thanks for chiming in on this sub-thread, I really enjoy reading your > posts.)
(And I enjoy using your parser! Not that I have to parse text so often, but when it comes, the "pythonicity" of pyparsing is a great thing!)
> My point is that the recommended strategy MAY work for those who write > end point applications (I consider maintaining 2 branches to be in the > "not working" category), but it does NOT WORK for people who maintain > modules for other people to use, because those people may be on a > range of Python versions that extend beyond 2.6-3.0. So if I upgrade > my module to 2.6, those running on earlier versions can no longer use > it. At some point in the future, I'll probably be able to say "no > more support for pre-2.6", but it is a bit early to start saying that > now.
> Likewise, I don't want to say "no support for 3.0" - people DO want to > try 3.0 out, and I WANT them to want and be able to use my module too.
> Given the recommended strategy, and ruling out dual codebase, whom do > I tell that they can't use the next version of my module?
Ok, code that is "2.6 compatible" doesn't mean that it only runs on 2.6... I'm *trying* to write code that is "2to3 friendly" but anyway compatible with older Python versions, and it should not require 2.6 to run. That means not using "with" as a variable name, for example. (And on the other side, also refrain from using some new 2.6 features like class decorators and binary literals) I hope the final version of the 2to3 tool will be a little more robust - or at least, that one will always be able to write code in a way that it can handle (and I *dont* want to maintain a 2.x and 3.x branches of any code either) Based on my limited experience I'd say that this approach *could* work, that is, write the code base for 2.x (x >= 3, in my case) and automatically convert to 3.0. That last stage may fail, but -I hope!- not so often in the future. As always, YMMV... Also note that I *don't* write code for other developers (thanks God!), just final users (with Python 2.3/4/5)
> Again, to me, this is a non-issue because I've been able to create a > cross-version compatible single codebase for pyparsing. But it was a > bit dicey there for a while, and I think other module developers/ > maintainers may not be so lucky.
That's a bit tricky at least. How did you manage to avoid problems with (string/unicode) and (bytes/string) in 3.0?
> So, I feel that the recommended strategy was devised with a narrow > group of developers in mind, and leaves module developers/maintainers, > who wish to target as broad a set of users as possible, faced with > choosing one of these strategies: > - create (if possible) single cross-version compatible code > - forego support of 3.0 users > - discontinue pre-2.6 support for future versions of their module > - maintain dual codebase
I hope the first alternative will be actually viable, perhaps with help from tools like 2to3...
