Divmod Combinator

[[Image(http://divmod.org/tracdocs/combinator_whtbck.png, right)]]

Combinator is a tool that Divmod Python programmers use to manage multiple branches of our software. It integrates with Subversion.

It can be used to manage any number of branches with any number of projects. It sets up your Python sys.path to point at the appropriate directories for the set of branches you are currently working on. It also sets up your PATH environment variable so that you can access any scripts that come along with those projects.

It is mainly of interest if you are checking code out of SVN: users of installed versions of Divmod software can probably ignore this project (for now).


Combinator does not currently work with SVN version 1.2 due to changes in the way SVN stores its local repository. See #2144 for details.


Subversion is a nice development system, but some tasks are unnecessarily difficult. In particular, as we migrated from CVS to SVN, we discovered that there are some operations which were impractically difficult in CVS but simple in SVN, such as creating branches, but while the implementation of managing and merging branches was adequate, there were too much flexibility, and too many ways to subtly incorrectly merge a branch.

As one example of such a problem, in SVN one must always pass the revision where the branch was created on trunk as an argument to the merge command, and determining that number involves reading the output of another long-running command. Some branches cannot be merged in this manner, depending on where the branch was originally created from.

We developed some idioms for avoiding common errors during merge and encoded them in a set of shell scripts. Then we discovered another set of common problems: often developers working on a branch would do a bunch of work, and then find themselves mystified that their changes did not seem to be taking effect, due to a mismatch between the environment of their development tools and the shells where test commands were being run.

Combinator began as a set of idioms and shell scripts and has evolved into a set of Python tools which enforce a simple workflow for using SVN and Python together to work on projects that use branches to gather changes together while eliminating common errors.


Combinator is in the Divmod repository.

If you want to use it without the rest of the Divmod projects, see the CombinatorTutorial.


Start with [source:trunk/Combinator/README.txt README.txt] to get your environment set up.


if you follow the UNIX setup instructions and an exception is raised along the lines of OSError: [Errno 2] No such file or directory: ‘/home/YOURNAME/.local/lib/python2.4/site-packages’, you should update to the latest trunk revision of Combinator - this bug has been fixed!

CombinatorTutorial is a guide to typical Combinator use including setting up an SVN repository to play with.

Reading about [wiki:UltimateQualityDevelopmentSystem our development process] is likely to give you some insight into how it’s intended to be used.


chbranch is the tool for switching to a different branch. Provide chbranch with a project name and branch name and it will modify all Combinator-enabled environments so that Python imports are satisfied from that branch of the project. If necessary, the branch will be checked out.


mkbranch is the tool for creating new branches. Provide mkbranch with a project name and branch name and it will create a new branch with that name, switch a copy of trunk to it, and do the equivalent of a chbranch to the new branch.


unbranch is the tool for merging a branch’s changes into trunk. First, use chbranch to change to the branch to be merged. Then, make sure that the trunk working copy either contains no changes or contains only changes which you want included in the merge (note: it is strongly, strongly recommended that if the merge will be committed that the trunk working copy contain no changes). Finally, run unbranch with the project name and the changes from the branch will be merged into the trunk working copy. They will not be committed automatically.

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