Forking baazar to add Python 3.x support

Chris Hecker checker at
Fri Mar 7 07:08:47 UTC 2014

Yeah, bzr has enough troubles with active support already, suddenly 
breaking everything seems like a terrible idea.


On 2014-03-06 22:53, William Grant wrote:
> On 07/03/14 11:28, Richard Wilbur wrote:
>> On Thu, Mar 6, 2014 at 7:05 AM, Bob Tanner <tanner at> wrote:
>>> I think dropping support for Python 2 would be a mistake at this point in
>>> time.
>> What reason(s) did you have in mind?
> Bazaar isn't just an application, but a library too, and the centre of a
> plugin ecosystem. An immediate breaking transition from Python 2 to 3
> would render all plugins and consumers of bzrlib unusable until they
> were ported -- and bzrlib consumers might not be portable to 3 in the
> short term if they depend on other 2-only libraries. The Python 2
> version of Bazaar would end up being maintained in parallel, scarily
> similar to the Python 2 vs 3 situation itself.
> Additionally, porting all 360,000 lines of Bazaar code at once is going
> to be time-consuming and fraught with bugs. It's likely far more
> practical to gradually port the various modules to 2+3 from the bottom
> up, leaving the test suite runnable on 2 to ensure that the partially
> ported project still works as a whole, throughout the long-term port
> process.
>> My understanding of the differences between Python 2 and Python 3
>> imply that depending on the level of coding sophistication it could
>> require significant work to support both in the same files.  Then
>> again, this could also be a good step in the right direction for the
>> bzr code base.  Evidently Armin Ronacher's python-modernize[1] is a
>> tool that can help with this process.
>> I can think of a few reasons it could be a real challenge to port bzr
>> to Python 3:
>> 1.  bzr currently represents a relatively mature software project with
>> a non-trivial volume of Python 2 code.  Any syntax changes may affect
>> a lot of code requiring significant re-factoring.  (The 2to3 tool
>> should help here.)
> 2to3 is almost always a bad idea, and I'd only ever consider it for a
> leaf application. The syntax changes are small enough that it's usually
> easy to write code that runs on 2.6+ and 3.2+ simultaneously, and there
> are many helper libraries around to deal with the semantic differences.
>> 2.  Any changes in semantics that don't break syntax won't be caught
>> by the language, so will require tracking down as bugs or failed test
>> cases.  (Anyone familiar with the 2to3 tool's track record on these
>> types of changes?)
> Bazaar fortunately has an excellent test suite, which can be run on each
> module as it's ported.
>> 3.  Library dependencies will need to be updated.  Libraries that
>> haven't been ported to Python 3 will require porting or re-factoring
>> the bzr interface to use a library that already supports Python 3.
> Core Bazaar doesn't have many external dependencies, so this shouldn't
> be a huge problem.
>> Nevertheless, Python 3.x is receiving the bulk of the new development
>> effort and cleans up Unicode/encoding handling for strings, among many
>> other things.[2]
> Python 3 is certainly the future. But in a lot of places it's still just
> that -- in the future. Python 2 will remain in the present for many
> users for a good few years, and forcing people who are stuck on 2 to
> fork Bazaar isn't going to do much good for anyone.
> William.

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