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<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 3. Packaged Modules</title><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="home" href="index.html" title="Debian Python Policy" /><link rel="up" href="index.html" title="Debian Python Policy" /><link rel="prev" href="python.html" title="Chapter 2. Python Packaging" /><link rel="next" href="programs.html" title="Chapter 4. Python Programs" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 3. Packaged Modules</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="python.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="programs.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a id="module_packages"></a>Chapter 3. Packaged Modules</h1></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="section"><a href="module_packages.html#idm319">3.1. Types of Python Modules</a></span></dt><dt><span class="section"><a href="module_packages.html#wheels">3.2. Wheels</a></span></dt><dt><span class="section"><a href="module_packages.html#package_names">3.3. Module Package Names</a></span></dt><dt><span class="section"><a href="module_packages.html#specifying_versions">3.4. Specifying Supported Versions</a></span></dt><dt><span class="section"><a href="module_packages.html#dependencies">3.5. Dependencies</a></span></dt><dt><span class="section"><a href="module_packages.html#provides">3.6. Provides</a></span></dt><dt><span class="section"><a href="module_packages.html#byte_compilation">3.7. Modules Byte-Compilation</a></span></dt></dl></div><p> The goal of these policies is to reduce the work necessary for Python transitions. Python modules are internally very dependent on a specific Python version. However, we want to automate recompiling modules when possible, either during the upgrade itself (re-compiling bytecode files <code class="filename">*.pyc</code> and <code class="filename">*.pyo</code>) or shortly thereafter with automated rebuilds (to handle C extensions). These policies encourage automated dependency generation and loose version bounds whenever possible. </p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="idm319"></a>3.1. Types of Python Modules</h2></div></div></div><p> There are two kinds of Python modules, "pure" Python modules, and extension modules. Pure Python modules are Python source code that generally works across many versions of Python. Extensions are C code compiled and linked against a specific version of the Python runtime, and so can only be used by one version of Python. </p><p> Debian Python does not link extensions to <code class="filename">libpython</code> (as is done in some operating systems). Symbols are resolved by <code class="filename">/usr/bin/python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em></code> which is not linked to <code class="filename">libpython</code>. </p><p> Python packages are a way of structuring Python’s module namespace by using “dotted module names”. See <a class="ulink" href="https://docs.python.org/3/glossary.html#term-package" target="_blank">Python's glossary</a> for details on how packages are defined in Python terms (a package in the Python sense is unrelated to a Debian package). Python packages must be packaged into the same directory (as done by upstream). Splitting components of a package across directories changes the import order and may confuse documentation tools and IDEs. </p><p> There are two ways to distribute Python modules. Public modules are installed in a public directory as listed in <a class="xref" href="python.html#paths" title="2.5. Module Path">Section 2.5, “Module Path”</a>. They are accessible to any program. Private modules are installed in a private directory such as <code class="filename">/usr/share/<em class="replaceable"><code>package-name</code></em></code> or <code class="filename">/usr/lib/<em class="replaceable"><code>package-name</code></em></code>. They are generally only accessible to a specific program or suite of programs included in the same package. </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="wheels"></a>3.2. Wheels</h2></div></div></div><p> <a class="ulink" href="https://www.python.org/dev/peps/pep-0427/" target="_blank">PEP 427</a> defines a built-package format called "wheels", which is a Zip format archive containing Python code and a <code class="filename">*.dist-info</code> metadata directory, in a single file named with the <code class="filename">.whl</code> suffix. As Zip files, wheels containing pure Python can be put on sys.path and modules in the wheel can be imported directly by Python's <code class="literal">import</code> statement. (Importing extension modules from wheels is not yet supported as of Python 3.4.) </p><p> Except as described below, packages must not build or provide wheels. They are redundant to the established way of providing Python libraries to Debian users, take no advantage of distro-based tools, and are less convenient to use. E.g. they must be explicitly added to <code class="literal">sys.path</code>, cannot be easily grepped, and stack traces through Zip files are more difficult to debug. </p><p> A very limited set of wheel packages are available in the archive, but these support the narrow purpose of enabling the <code class="filename">pip</code>, <code class="filename">virtualenv</code>, and <code class="filename">pyvenv</code> tools in a Debian policy compliant way. These packages build their own dependent wheels through the use of the <code class="filename">dirtbike</code> "rewheeling" tool, which takes installed Debian packages and turns them back into wheels. Only universal wheels (i.e. pure-Python, Python 3 and 2 compatible packages) are supported. Since only the programs that require wheels need build them, only they may provide <code class="filename">-whl</code> packages, e.g. <code class="literal">python3-pip-whl</code>. </p><p> When these binary packages are installed, <code class="filename">*.whl</code> files must be placed in the <code class="filename">/usr/share/python-wheels</code> directory. The location inside a virtual environment will be rooted in the virtual environment, instead of <code class="filename">/usr</code>. </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="package_names"></a>3.3. Module Package Names</h2></div></div></div><p> Public Python modules must be packaged separately by major Python version, to preserve run time separation between Python 2 and Python 3. </p><p> Public Python 3 modules used by other packages must have their binary package name prefixed with <code class="literal">python3-</code>. It is recommended to use this prefix for all packages with public modules as they may be used by other packages in the future. </p><p> The binary package for module <em class="replaceable"><code>foo</code></em> should preferably be named <code class="literal">python3-<em class="replaceable"><code>foo</code></em></code>, if the module name allows. This is not required if the binary package installs multiple modules, in which case the maintainer shall choose the name of the module which best represents the package. </p><p> For subpackages such as <em class="replaceable"><code>foo.bar</code></em>, the recommendation is to name the binary package <code class="literal">python3-<em class="replaceable"><code>foo.bar</code></em></code>. </p><p> Such a package should support the current Debian Python version, and more if possible (there are several tools to help implement this, see <a class="xref" href="packaging_tools.html" title="Appendix B. Packaging Tools">Appendix B, <em>Packaging Tools</em></a>). For example, if Python 3.3, 3.4, and 3.5 are supported, the Python statement </p><pre class="programlisting"> import foo </pre><p> should import the module when the program interpreter is any of <code class="filename">/usr/bin/python3.3</code>, <code class="filename">/usr/bin/python3.4</code>, and <code class="filename">/usr/bin/python3.5</code>. This requirement also applies to extension modules; binaries for all the supported Python versions should be included in a single package. </p><p> Packages intended for use with Django (<code class="literal">python3-django</code> are installed in the same namespace as other python packages for a variety of reasons. Many such packages are named django_$name upstream. These are then packaged as <code class="literal">python3-django-$name</code>. This makes it clear that they are intended for use with Django and not general purpose Python modules. Debian maintainers are encouraged to work with their upstreams to support consistent use of this approach. </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="specifying_versions"></a>3.4. Specifying Supported Versions</h2></div></div></div><p> The <code class="filename">debian/control</code> source paragraph may contain optional fields to specify the versions of Python the package supports. </p><p> The optional <code class="literal">X-Python3-Version</code> field specifies the versions of Python 3 supported. When not specified, it defaults to all currently supported Python 3 versions. </p><p> Similarly, the optional fields <code class="literal">X-Python-Version</code> or <code class="literal">XS-Python-Version</code> were used to specify the versions of Python 2 supported by the source package. They are obsolete and must be removed. </p><p> These fields are used by some packaging scripts to automatically generate appropriate Depends and Provides lines. The format of the field may be one of the following: </p><pre class="programlisting"> X-Python3-Version: >= X.Y X-Python3-Version: >= A.B, << X.Y XS-Python-Version: A.B, X.Y </pre><p> </p><p> The keyword <code class="literal">all</code> is no longer to be used since using version numbers is clearer than <code class="literal">all</code> and encodes more information. The keyword <code class="literal">all</code> must be ignored for Python 3 versions. </p><p> A comma-separated list of multiple individual versions (e.g. <code class="literal">3.3, 3.4, 3.5</code>) in <code class="literal">XS-Python-Version</code> will continue to be supported, but is not recommended. The use of multiple individual versions in <code class="literal">X-Python-Version</code> or <code class="literal">X-Python3-Version</code> is not supported for Wheezy and later releases. </p><p> The keyword <code class="literal">current</code> has been deprecated and must not be used. It must be ignored for Python 3 versions. </p><p> The use of <code class="literal">XB-Python-Version</code> in the binary package paragraphs of <code class="filename">debian/control</code> file has been deprecated and should be removed in the normal course of package updates. It never achieved sufficient deployment to support its intended purpose of managing Python transitions. This purpose can be adequately accomplished by examining package dependencies. </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="dependencies"></a>3.5. Dependencies</h2></div></div></div><p> Any package that installs modules for the default Python version (or many versions including the default) as described in <a class="xref" href="module_packages.html#package_names" title="3.3. Module Package Names">Section 3.3, “Module Package Names”</a>, must declare a dependency on the default Python runtime package. If it requires other modules to work, the package must declare dependencies on the corresponding packaged modules. The package must not declare dependency on any version-specific Python runtime or module package. </p><p> For Python 3, the correct dependencies are <code class="literal">Depends: python3 (>= 3.<em class="replaceable"><code>Y</code></em>)</code> and any corresponding <code class="literal">python3-<em class="replaceable"><code>foo</code></em></code> packages. </p><p> If any Python 2 packages remain, the correct dependencies are <code class="literal">Depends: python2 (>= 2.<em class="replaceable"><code>Y</code></em>)</code> and any corresponding <code class="literal">python2-<em class="replaceable"><code>foo</code></em></code> packages. </p><p> Any package that installs Python modules or Python 3 binary extensions must also declare a maximum version it supports as currently built. This is accomplished by declaring a maximum version constraint strictly less than one higher than the current maximum version, i.e. <code class="literal">Depends: python3 (<< <em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em>)</code>. </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="provides"></a>3.6. Provides</h2></div></div></div><p> Binary packages that declare Provides dependencies of the form <code class="literal">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em>-<em class="replaceable"><code>foo</code></em></code> were never supported for Python 3. They should be removed in the normal course of package updates. Future provision of values for the substituation variable <code class="literal">python:Provides</code> is not guaranteed. </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="byte_compilation"></a>3.7. Modules Byte-Compilation</h2></div></div></div><p> If a binary package provides any binary-independent modules (<code class="filename"><em class="replaceable"><code>foo</code></em>.py</code> files), the corresponding byte-compiled modules (<code class="filename"><em class="replaceable"><code>foo</code></em>.pyc</code> files) and optimized modules (<code class="filename"><em class="replaceable"><code>foo</code></em>.pyo</code> files) must not ship in the package. Instead, they should be generated in the package's post-install script, and removed in the package's pre-remove script. The package's prerm has to make sure that both <code class="filename"><em class="replaceable"><code>foo</code></em>.pyc</code> and <code class="filename"><em class="replaceable"><code>foo</code></em>.pyo</code> are removed. </p><p> A binary package should only byte-compile the files which belong to the package. </p><p> The file <code class="filename">/etc/python/debian_config</code> allows configuration how modules should be byte-compiled. The post-install scripts should respect these settings. </p><p> Pure Python modules in private installation directories that are byte-compiled with the default Python version must be forcefully byte-compiled again when the default Python version changes. </p><p> Public Python extensions should be bin-NMUed. </p><p> Private Python extensions should be subject to binary NMUs every time the default interpreter changes, unless the extension is updated through a <code class="filename">*.rtupdate</code> script. </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="python.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="programs.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 2. 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