Getting Started

This tutorial will guide you through setting up your first project using dh-virtualenv. Having some knowledge on how Debian packages work might help, but it is not a mandatory requirement when working on simple projects.

You also need some basic build tools, so you should install these packages:

sudo apt install build-essential debhelper devscripts equivs

These are only required on the build host, not the target hosts you later install the built packages on.

If you perform your package builds in a Docker container, you can also skip installing these tools, because then only docker-ce is needed.

Step 1: Install dh-virtualenv

Overview

In order to use it, you need to install dh-virtualenv as a debhelper add-on on the build host. For Debian and Ubuntu, there are pre-built packages for the 1.0 version available – note that some of this info might get outdated over time, so take extra care to check the version numbers you’re actually getting vs. what features you need.

The following paragraphs describe the various installation options, including building from source when your specific environment provides no packages or only older versions.

Using pre-1.1 versions is possible, but you don’t get all features described in this document, and not all projects using dh-virtualenv might work with older versions (check their documentation).

Package installation from OS repositories

On Debian and Ubuntu, dh-virtualenv is available from their package repositories:

sudo apt update
sudo apt install dh-virtualenv

It is also possible to get newer versions from Debian testing or unstable (sid) or recent releases in the official Ubuntu repositories. Since dh-virtualenv has the all architecture (contains no native code), that is generally possible, but you might need to take extra care of dependencies. The recommendation is to only follow that route in Docker container builds, where manipulating dependencies has no lasting effect – don’t do that on your workstation.

Build your own package

For all other platforms you have to build and install the tool yourself. The easiest way (since v1.1) is to build the package using Docker with the invoke bdist_deb command in a boot-strapped working directory, see the README for details on that. Using Docker also allows cross-distribution builds.

Otherwise, after you have cloned the repository, you must install build tools and dependencies on your worksatation, and then start the build:

# Install needed packages
sudo apt install devscripts git
# Clone git repository
git clone https://salsa.debian.org/python-team/packages/dh-virtualenv.git
# Change into working directory
cd dh-virtualenv
# This will install build dependencies
sudo apt build-dep ./
# Build the *dh-virtualenv* package
dpkg-buildpackage -us -uc -b

# And finally, install it (apt also pulls in its dependencies)
sudo apt install ../dh-virtualenv_<version>_all.deb

Step 2: Set up packaging for your project

Grab your favourite Python project you want to use dh-virtualenv with and set it up. Only requirement is that your project has a somewhat sane setup.py and requirements listed in a requirements.txt file. Note however that defining any requirements is not mandatory, if you have none.

Instead of following all the steps outlined below, you can use cookiecutters (project templates) to quickly create the needed information in the debian/ directory for any existing project.

  • dh-virtualenv-mold is a cookiecutter template to add easy Debianization to any existing Python project.

  • debianized-pypi-mold does the same for 3rd party software released to PyPI which you want to package for deployment.

See the related READMEs for details.

For the manual way, start with defining the Debian packaging metadata for your software. To do this, create a directory called debian in the project root.

To be able to build a debian package, a few files are needed. First we need a file that tells what our project is about, a file called control. Create a debian/control file similar to the following:

Source: my-awesome-python-software
Section: python
Maintainer: Matt Maintainer <matt@example.com>
Build-Depends: debhelper-compat (= 13), dh-virtualenv, python3
Standards-Version: 4.7.4

Package: my-awesome-python-software
Architecture: any
Depends: python3, ${misc:Depends}, ${shlibs:Depends}
Description: A short summary of what this is.
 Further indented lines can contain extra information.
 .
 A single dot separates paragraphs.

The debhelper-compat (= 13) build dependency sets the debhelper compatibility level; 13 is the current recommended one, and no separate debian/compat file is needed.

The control file is used to define the build dependencies, so if you are building a package that requires for example lxml, make sure you define libxml2-dev in Build-Depends.

Depends in the 2nd section is used to define run-time dependencies. The debhelper magic will usually take care of that via the ${misc:Depends} you see above.

To help keeping your installed virtualenv in sync with the host’s Python interpreter in case of updates, create a file named debian/«pkgname».triggers, where «pkgname» is what you named your package in the control file. It triggers a special script whenever the Python binary changes; don’t worry, that script is provided by dh-virtualenv automatically.

«pkgname».triggers

# Register interest in Python interpreter changes; and don't make the
# Python package dependent on the virtualenv package processing (noawait)
interest-noawait /usr/bin/python3

# Also provide a symbolic trigger for all dh-virtualenv packages
interest dh-virtualenv-interpreter-update

That file must end with a new-line – if your editor is misconfigured to eat the end of the last line in a file, you better fix that.

Note that if you provide a custom postinst script with your package, then don’t forget to put the #DEBHELPER# marker into it, else the trigger script will be missing. The same applies to other maintainer scripts.

Next, we need a changelog file. It is basically a documentation of changes in your package plus the source for version number for Debian package builder. Here’s a short sample changelog to be entered in debian/changelog:

my-awesome-python-software (0.1-1) unstable; urgency=low

  * Initial public release

 -- Matt Maintainer <matt@example.com>  Fri, 01 Nov 2013 17:00:00 +0200

You don’t need to create this file by hand, a handy tool called dch exists for entering new changelog entries.

Now, the last bit left is adding the debian/rules file. This file is usually an executable Makefile that Debian uses to build the package. The content for that is fairly simple:

#!/usr/bin/make -f

%:
      dh $@ --with python-virtualenv

And there we go, debianization of your new package is ready!

Tip

Do not forget to git add the debian/ directory before you build for the first time, because generated files will be added there that you don’t want in your source code repository.

Step 3: Build your project

Now you can just build your project by running ( deactivate ; dpkg-buildpackage -us -uc -b ). Enjoy your newly baked dh-virtualenv backed project! ☺