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# Working from Twisted’s Subversion repository

If you’re going to be doing development on Twisted itself, or if you want to take advantage of bleeding-edge features (or bug fixes) that are not yet available in a numbered release, you’ll probably want to check out a tree from the Twisted Subversion repository. The Trunk is where all current development takes place.

This document lists some useful tips for working on this cutting edge.

## Checkout

Subversion tutorials can be found elsewhere, see in particular the Subversion homepage . The relevant data you need to check out a copy of the Twisted tree is available on the development page , and is as follows:

    $ svn co svn://svn.twistedmatrix.com/svn/Twisted/trunk Twisted

## Alternate tree names

By using `svn co svn://svn.twistedmatrix.com/svn/Twisted/trunk otherdir` , you can put the workspace tree in a directory other than “Twisted” . I do this (with a name like “Twisted-Subversion” ) to remind myself that this tree comes from Subversion and not from a released version (like “Twisted-1.0.5” ). This practice can cause a few problems, because there are a few places in the Twisted tree that need to know where the tree starts, so they can add it to `sys.path` without requiring the user manually set their PYTHONPATH. These functions walk the current directory up to the root, looking for a directory named “Twisted” (sometimes exactly that, sometimes with a `.startswith` test). Generally these are test scripts or other administrative tools which expect to be launched from somewhere inside the tree (but not necessarily from the top).

If you rename the tree to something other than `Twisted` , these tools may wind up trying to use Twisted source files from /usr/lib/python2.5 or elsewhere on the default `sys.path` . Normally this won’t matter, but it is good to be aware of the issue in case you run into problems.

`twisted/test/process_twisted.py` is one of these programs.

## Combinator

In order to simplify the use of Subversion, we typically use Divmod Combinator . You may find it to be useful, too. In particular, because Twisted uses branches for almost all feature development, if you plan to contribute to Twisted you will probably find Combinator very useful. For more details, see the Combinator website, as well as the UQDS page.

## Compiling C extensions

There are currently several C extension modules in Twisted: `twisted.internet.cfsupport` , `twisted.internet.iocpreactor._iocp` , and `twisted.python._epoll` . These modules are optional, but you’ll have to compile them if you want to experience their features, performance improvements, or bugs. There are two approaches.

The first is to do a regular distutils `./setup.py build` , which will create a directory under `build/` to hold both the generated `.so` files as well as a copy of the 600-odd `.py` files that make up Twisted. If you do this, you will need to set your PYTHONPATH to something like `MyDir/Twisted/build/lib.linux-i686-2.5` in order to run code against the Subversion twisted (as opposed to whatever’s installed in `/usr/lib/python2.5` or wherever python usually looks). In addition, you will need to re-run the `build` command every time you change a `.py` file. The `build/lib.foo` directory is a copy of the main tree, and that copy is only updated when you re-run `setup.py build` . It is easy to forget this and then wonder why your code changes aren’t being expressed.

The second technique is to build the C modules in place, and point your PYTHONPATH at the top of the tree, like `MyDir/Twisted` . This way you’re using the .py files in place too, removing the confusion a forgotten rebuild could cause with the separate build/ directory above. To build the C modules in place, do `./setup.py build_ext -i` . You only need to re-run this command when you change the C files. Note that `setup.py` is not Make, it does not always get the dependencies right (`.h` files in particular), so if you are hacking on the cReactor you may need to manually delete the `.o` files before doing a rebuild. Also note that doing a `setup.py clean` will remove the `.o` files but not the final `.so` files, they must be deleted by hand.

## Running tests

To run the full unit-test suite, do:

    ./bin/trial twisted

To run a single test file (like `twisted/test/test_defer.py` ), do one of:

    ./bin/trial twisted.test.test_defer

or

    ./bin/trial twisted/test/test_defer.py

To run any tests that are related to a code file, like `twisted/protocols/imap4.py` , do:

    ./bin/trial --testmodule twisted/mail/imap4.py

This depends upon the `.py` file having an appropriate “test-case-name” tag that indicates which test cases provide coverage. See the Test Standards document for details about using “test-case-name” . In this example, the `twisted.mail.test.test_imap` test will be run.

Many tests create temporary files in /tmp or ./_trial_temp, but everything in /tmp should be deleted when the test finishes. Sometimes these cleanup calls are commented out by mistake, so if you see a stray `/tmp/@12345.1` directory, it is probably from `test_dirdbm` or `test_popsicle` . Look for an `rmtree` that has been commented out and complain to the last developer who touched that file.

## Building docs

Twisted documentation (not including the automatically-generated API docs) is generated by Sphinx . The docs are written in Restructured Text (`.rst`) and translated into `.html` files by the `bin/admin/build-docs` script.

To build the HTML form of the docs into the `doc/` directory, do the following:

    ./bin/admin/build-docs .

## Committing and Post-commit Hooks

Twisted uses a customized trac-post-commit-hook to enable ticket updates based on svn commit logs. When making a branch for a ticket, the branch name should end in `-<ticket number>` , for example `my-branch-9999` . This will add a ticket comment containing a changeset link and branch name. To make your commit message show up as a comment on a Trac ticket, add a `refs #<ticket number>` line at the bottom of your commit message. To automatically close a ticket on Trac as `Fixed` and add a comment with the closing commit message, add a `Fixes: #<ticket number>` line to your commit message. In general, a commit message closing a ticket looks like this:

    Merge my-branch-9999: A single-line summary.

    Author: jesstess
    Reviewers: exarkun, glyph
    Fixes: #9999

    My longer description of the changes made.

The Twisted Coding Standard elaborates on commit messages and source control.

## Emacs

A minor mode for development with Twisted using Emacs is available. See `twisted-dev.el` , provided by twisted-emacs , for several utility functions which make it easier to grep for methods, run test cases, etc.

## Building Debian packages

Our support for building Debian packages has fallen into disrepair. We would very much like to restore this functionality, but until we do so, if you are interested in this, you are on your own. See stdeb for one possible approach to this.