py2deb: Python to Debian package converter

.. image:: https://travis-ci.org/paylogic/py2deb.svg?branch=master :target: https://travis-ci.org/paylogic/py2deb

.. image:: https://coveralls.io/repos/paylogic/py2deb/badge.svg?branch=master :target: https://coveralls.io/r/paylogic/py2deb?branch=master

The Python package py2deb_ converts Python source distributions to Debian binary packages (the ones used for installation). It uses pip-accel_ (based on pip_) to download, unpack and compile Python packages. Because of this py2deb_ is compatible with the command line interface of the pip install command. For example you can specify packages to convert as command line arguments but you can also use requirement files_ if you want.

During the conversion process dependencies are automatically taken into account and converted as well so you don't actually have to use requirement files including transitive dependencies. In fact you might prefer not explicitly listing your transitive dependencies in requirement files because py2deb_ will translate the version constraints of Python packages into Debian package relationships.

The py2deb_ package is currently tested on CPython_ 2.7, 3.5, 3.6, 3.7 and PyPy_ 2 and 3. Unfortunately Python 3.8+ is not yet supported (see below). For usage instructions please refer to the documentation hosted on Read The Docs_.

.. contents:: :local:

Installation

The py2deb_ package is available on PyPI_, so installation is very simple:

.. code-block:: console

$ pip install py2deb

There are some system dependencies which you have to install as well:

.. code-block:: console

$ sudo apt-get install dpkg-dev fakeroot

Optionally you can also install Lintian_ (which is not a hard dependency but more of a "nice to have"):

.. code-block:: console

$ sudo apt-get install lintian

When Lintian is installed it will be run automatically to sanity check converted packages. This slows down the conversion process somewhat but can be very useful, especially when working on py2deb itself. Currently py2deb doesn't fail when Lintian reports errors, this is due to the unorthodox ways in which py2deb can be used. This may change in the future as py2deb becomes more mature.

Usage

There are two ways to use the py2deb_ package: As the command line program py2deb and as a Python API. For details about the Python API please refer to the API documentation hosted on Read the Docs_. The command line interface is described below.

Command line

.. A DRY solution to avoid duplication of the `py2deb --help' text:
..
.. [[[cog
.. from humanfriendly.usage import inject_usage
.. inject_usage('py2deb.cli')
.. ]]]

**Usage:** `py2deb [OPTIONS] ...`

Convert Python packages to Debian packages according to the given
command line options (see below). The command line arguments are the
same as accepted by the "pip install" command because py2deb invokes
pip during the conversion process. This means you can name the
package(s) to convert on the command line but you can also use
"requirement files" if you prefer.

If you want to pass command line options to pip (e.g. because you want
to use a custom index URL or a requirements file) then you will need
to tell py2deb where the options for py2deb stop and the options for
pip begin. In such cases you can use the following syntax:

.. code-block:: sh

  $ py2deb -r /tmp -- -r requirements.txt

So the "--" marker separates the py2deb options from the pip options.

**Supported options:**

.. csv-table::
   :header: Option, Description
   :widths: 30, 70


   "``-c``, ``--config=FILENAME``","Load a configuration file. Because the command line arguments are processed
   in the given order, you have the choice and responsibility to decide if
   command line options override configuration file options or vice versa.
   Refer to the documentation for details on the configuration file format.
   
   The default configuration files /etc/py2deb.ini and ~/.py2deb.ini are
   automatically loaded if they exist. This happens before environment
   variables and command line options are processed.
   
   Can also be set using the environment variable ``$PY2DEB_CONFIG``."
   "``-r``, ``--repository=DIRECTORY``","Change the directory where \*.deb archives are stored. Defaults to
   the system wide temporary directory (which is usually /tmp). If
   this directory doesn't exist py2deb refuses to run.
   
   Can also be set using the environment variable ``$PY2DEB_REPOSITORY``."
   "``--use-system-package=PYTHON_PACKAGE_NAME,DEBIAN_PACKAGE_NAME``","Exclude a Python package (the name before the comma) from conversion and
   replace references to the Python package with a specific Debian package
   name. This allows you to use system packages for specific Python
   requirements."
   ``--name-prefix=PREFIX``,"Set the name prefix used during the name conversion from Python to
   Debian packages. Defaults to ""python"". The name prefix and package
   names are always delimited by a dash.
   
   Can also be set using the environment variable ``$PY2DEB_NAME_PREFIX``."
   ``--no-name-prefix=PYTHON_PACKAGE_NAME``,"Exclude a Python package from having the name prefix applied
   during the package name conversion. This is useful to avoid
   awkward repetitions."
   "``--rename=PYTHON_PACKAGE_NAME,DEBIAN_PACKAGE_NAME``","Override the package name conversion algorithm for the given pair
   of package names. Useful if you don't agree with the algorithm :-)"
   ``--install-prefix=DIRECTORY``,"Override the default system wide installation prefix. By setting
   this to anything other than ""/usr"" or ""/usr/local"" you change the
   way py2deb works. It will build packages with a file system layout
   similar to a Python virtual environment, except there will not be
   a Python executable: The packages are meant to be loaded by
   modifying Python's module search path. Refer to the documentation
   for details.
   
   Can also be set using the environment variable ``$PY2DEB_INSTALL_PREFIX``."
   "``--install-alternative=LINK,PATH``","Use Debian's ""update-alternatives"" system to add an executable
   that's installed in a custom installation prefix (see above) to
   the system wide executable search path. Refer to the documentation
   for details."
   ``--python-callback=EXPRESSION``,"Set a Python callback to be called during the conversion process. Refer to
   the documentation for details about the use of this feature and the syntax
   of ``EXPRESSION``.
   
   Can also be set using the environment variable ``$PY2DEB_CALLBACK``."
   ``--report-dependencies=FILENAME``,"Add the Debian relationships needed to depend on the converted
   package(s) to the given control file. If the control file already
   contains relationships the additional relationships will be added
   to the control file; they won't overwrite existing relationships."
   "``-y``, ``--yes``","Instruct pip-accel to automatically install build time dependencies
   where possible. Refer to the pip-accel documentation for details.
   
   Can also be set using the environment variable ``$PY2DEB_AUTO_INSTALL``."
   "``-v``, ``--verbose``",Make more noise :-).
   "``-h``, ``--help``",Show this message and exit.

.. [[[end]]]

Future improvements
-------------------

The following sections list possible improvements to the project:

.. contents::
   :local:

.. _Python 3.8+ compatibility:

Python 3.8+ compatibility

The py2deb_ project builds on top of pip-accel_, which was developed between 2013 and 2015 on top of pip >= 7.0, < 7.2. Since that time pip_ has grown enormously: At the time of writing (in August 2020) we're now at pip 20!

None of the improvements made between pip 7-20 are available in pip-accel and py2deb and this has become somewhat of a glaring issue that plenty of users have run into (see #17, #18, #27_ and #31_).

Known issues being caused by this include:

• The old pip version prevents Python 3.8+ compatibility.

• The old pip version doesn't know about python_requires metadata provided by PyPI and this forces users to maintain constraints files themselves, even though this shouldn't be necessary.

• While pip-accel supports installation from wheels, it was never exposed via the Python API and so py2deb lacks support for converting wheels (it currently needs source distributions).

The current state of affairs is best summarized in this comment_. I'm hoping to complete the upgrade to newer pip and pip-accel releases in the coming weeks (as of this writing in August 2020) but can't commit to a date.

.. _this comment: https://github.com/paylogic/py2deb/issues/18#issuecomment-633848582

Installation of system wide files

Find a way to facilitate (explicit / opt-in) installation of system wide files
(not related to Python per se) based on a Python distribution? This could
significantly reduce the need for "wrapper packages" that basically just pull
in packages converted by py2deb and drop a few configuration files into place.

:Related issues: See issue `#7`_ for a related discussion.

Conversion of binary wheels
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Investigate the feasability of supporting conversion of binary wheels. Slowly
but surely the Python community seems to be gravitating towards (binary) wheels
and once gravity has shifted we don't want to be left in the dust! 😉

Full PEP-440 compatibility
~~~~~~~~~~~~~~~~~~~~~~~~~~

Dive into PEP-440_ and see if it can be fully supported? Then `this question on
Reddit`_ can finally get a satisfying answer 🙂.

Similar projects
----------------

There are several projects out there that share similarities with py2deb, for
example I know of stdeb_, dh-virtualenv_ and fpm_. The documentation includes a
fairly `detailed comparison`_ with each of these projects.

Contact
-------

The latest version of py2deb is available on PyPI_ and GitHub_. The
documentation is hosted on `Read the Docs`_ and includes a changelog_. For
questions, bug reports, suggestions, etc. please create an issue on GitHub_.

License
-------

This software is licensed under the `MIT license`_.

© 2020 Peter Odding, Arjan Verwer and Paylogic International.

.. External references:
.. _CPython: https://en.wikipedia.org/wiki/CPython
.. _GitHub: https://github.com/paylogic/py2deb
.. _Lintian: http://en.wikipedia.org/wiki/Lintian
.. _MIT license: http://en.wikipedia.org/wiki/MIT_License
.. _PEP-440: https://www.python.org/dev/peps/pep-0440/
.. _Pillow: https://python-pillow.github.io/
.. _PyPI: https://pypi.org/project/py2deb
.. _PyPy: https://en.wikipedia.org/wiki/PyPy
.. _Read The Docs: https://py2deb.readthedocs.io
.. _changelog: https://py2deb.readthedocs.io/en/latest/changelog.html
.. _deb-pkg-tools: https://pypi.org/project/deb-pkg-tools
.. _detailed comparison: https://py2deb.readthedocs.io/en/latest/comparisons.html
.. _dh-virtualenv: https://github.com/spotify/dh-virtualenv
.. _fpm: https://github.com/jordansissel/fpm
.. _pip-accel: https://pypi.org/project/pip-accel
.. _pip: https://pypi.org/project/pip
.. _py2deb: https://pypi.org/project/py2deb
.. _python-imaging: https://packages.debian.org/search?keywords=python-imaging
.. _python-pil: https://packages.debian.org/search?keywords=python-pil
.. _requirement files: http://www.pip-installer.org/en/latest/cookbook.html#requirements-files
.. _stdeb: https://pypi.org/project/stdeb
.. _this question on Reddit: https://www.reddit.com/r/Python/comments/2x7s17/py2deb_python_to_debian_package_converter/coxyyzu
.. _#7: https://github.com/paylogic/py2deb/issues/7
.. _#17: https://github.com/paylogic/py2deb/issues/17
.. _#18: https://github.com/paylogic/py2deb/issues/18
.. _#27: https://github.com/paylogic/py2deb/issues/27
.. _#31: https://github.com/paylogic/py2deb/issues/31