Developing Morepath


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Install Morepath for development

First make sure you have virtualenv installed for Python 2.7.

Now create a new virtualenv somewhere for Morepath development:

$ virtualenv /path/to/ve_morepath

You should also be able to recycle an existing virtualenv, but this guarantees a clean one. Note that we skip activating the environment here, as this is just needed to initially bootstrap the Morepath buildout.

Clone Morepath from github and go to the morepath directory:

$ git clone
$ cd morepath

Now we need to run to set up buildout, using the Python from the virtualenv we’ve created before:

$ /path/to/ve_morepath/bin/python

This installs buildout, which can now set up the rest of the development environment:

$ bin/buildout

This downloads and installs various dependencies and tools. The commands you run in bin are all restricted to the virtualenv you set up before. There is therefore no need to refer to the virtualenv once you have the development environment going.

Running the tests

You can run the tests using py.test. Buildout has installed it for you in the bin subdirectory of your project:

$ bin/py.test morepath

To generate test coverage information as HTML do:

$ bin/py.test morepath --cov morepath --cov-report html

You can then point your web browser to the htmlcov/index.html file in the project directory and click on modules to see detailed coverage information.


The buildout also installs flake8, which is a tool that can do various checks for common Python mistakes using pyflakes and checks for PEP8 style compliance.

To do pyflakes and pep8 checking do:

$ bin/flake8 morepath


The buildout installs radon. This is a tool that can check various measures of code complexity.

To check for cyclomatic complexity (excluding the tests):

$ bin/radon cc morepath -e "morepath/tests*"

To filter for anything not ranked A:

$ bin/radon cc morepath --min B -e "morepath/tests*"

And to see the maintainability index:

$ bin/radon mi morepath -e "morepath/tests*"

Running the documentation tests

The documentation contains code. To check these code snippets, you can run this code using this command:

$ bin/sphinxpython bin/sphinx-build -b doctest doc doc/build/doctest

If you have Make installed, buildout generates for you a Makefile in the directory doc/build that you can use:

$ (cd doc/build; make doctest)

Building the HTML documentation

To build the HTML documentation (output in doc/build/html), run:

$ bin/sphinxbuilder


In some cases we have to make changes that break compatibility and break user code. We mark these in CHANGES.txt (CHANGES) using breaking change, deprecated or removed.

These entries should explain the change, and also tell the user what to do to upgrade their code. Do include an before/after code example as that makes it much easier, even if it’s a simple import change.

We like to keep things moving and reserve the right to introduce breaking changes. When we do make a breaking change it should be marked clearly in CHANGES.txt (CHANGES) with a Breaking change marker.

If it is not a great burden we use deprecations. Morepath in this case retains the old APIs but issues a deprecation warning. See Upgrading to a new Morepath version for the notes for end-users concerning this. Here is the deprecation procedure for developers:

  • Add a Deprecated entry in CHANGES.txt that describes what to do, as in a breaking change.

  • Issue a deprecation warning in the code that is deprecated.

  • Put a **Deprecated** entry in the docstring of whatever got deprecated with a brief comment on what to do.

  • Put an issue labeled remove deprecation in the tracker for one release milestone after the upcoming release that states we should remove the deprecation. Create the milestone if needed.

    This way we don’t maintain deprecated code and their warnings indefinitely – one release later we remove the backwards compatibility code and deprecation warnings.

  • Once we go and remove code, we repeat the information on what to do in a new Removed* entry in CHANGES.txt; treat it just like Breaking change and recycle the text written for the previous Deprecated entry for the stuff we’re now removing.