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<title>Alexis Métaireau</title>
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<div id="top">
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<p class="author"><a href="./about.html">Alexis Métaireau</a>'s thoughs</p>
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<ul class="links">
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<li><a href=".">↵ </a></li>
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</ul>
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</div>
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<div class="content clear">
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<h1>Introducing the distutils2 index crawlers</h1>
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<p class="date">Published on Tue 06 July 2010</p>
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<p>I'm working for about a month for distutils2, even if I was being a
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bit busy (as I had some class courses and exams to work on)</p>
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<p>I'll try do sum-up my general feelings here, and the work I've made
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so far. You can also find, if you're interested, my weekly
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summaries in
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<a class="reference external" href="http://wiki.notmyidea.org/distutils2_schedule">a dedicated wiki page</a>.</p>
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<div class="section" id="general-feelings">
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<h2>General feelings</h2>
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<p>First, and it's a really important point, the GSoC is going very
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well, for me as for other students, at least from my perspective.
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It's a pleasure to work with such enthusiast people, as this make
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the global atmosphere very pleasant to live.</p>
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<p>First of all, I've spent time to read the existing codebase, and to
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understand what we're going to do, and what's the rationale to do
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so.</p>
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<p>It's really clear for me now: what we're building is the
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foundations of a packaging infrastructure in python. The fact is
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that many projects co-exists, and comes all with their good
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concepts. Distutils2 tries to take the interesting parts of all,
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and to provide it in the python standard libs, respecting the
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recently written PEP about packaging.</p>
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<p>With distutils2, it will be simpler to make "things" compatible. So
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if you think about a new way to deal with distributions and
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packaging in python, you can use the Distutils2 APIs to do so.</p>
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</div>
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<div class="section" id="tasks">
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<h2>Tasks</h2>
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<p>My main task while working on distutils2 is to provide an
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installation and an un-installation command, as described in PEP
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376. For this, I first need to get informations about the existing
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distributions (what's their version, name, metadata, dependencies,
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etc.)</p>
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<p>The main index, you probably know and use, is PyPI. You can access
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it at <a class="reference external" href="http://pypi.python.org">http://pypi.python.org</a>.</p>
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</div>
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<div class="section" id="pypi-index-crawling">
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<h2>PyPI index crawling</h2>
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<p>There is two ways to get these informations from PyPI: using the
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simple API, or via xml-rpc calls.</p>
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<p>A goal was to use the version specifiers defined
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in`PEP 345 <<a class="reference external" href="http://www.python.org/dev/peps/pep-0345/">http://www.python.org/dev/peps/pep-0345/</a>>`_ and to
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provides a way to sort the grabbed distributions depending our
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needs, to pick the version we want/need.</p>
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<div class="section" id="using-the-simple-api">
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<h3>Using the simple API</h3>
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<p>The simple API is composed of HTML pages you can access at
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<a class="reference external" href="http://pypi.python.org/simple/">http://pypi.python.org/simple/</a>.</p>
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<p>Distribute and Setuptools already provides a crawler for that, but
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it deals with their internal mechanisms, and I found that the code
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was not so clear as I want, that's why I've preferred to pick up
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the good ideas, and some implementation details, plus re-thinking
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the global architecture.</p>
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<p>The rules are simple: each project have a dedicated page, which
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allows us to get informations about:</p>
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<ul class="simple">
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<li>the distribution download locations (for some versions)</li>
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<li>homepage links</li>
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<li>some other useful informations, as the bugtracker address, for
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instance.</li>
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</ul>
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<p>If you want to find all the distributions of the "EggsAndSpam"
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project, you could do the following (do not take so attention to
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the names here, as the API will probably change a bit):</p>
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<div class="highlight"><pre><span class="o">>>></span> <span class="n">index</span> <span class="o">=</span> <span class="n">SimpleIndex</span><span class="p">()</span>
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<span class="o">>>></span> <span class="n">index</span><span class="o">.</span><span class="n">find</span><span class="p">(</span><span class="s">"EggsAndSpam"</span><span class="p">)</span>
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<span class="p">[</span><span class="n">EggsAndSpam</span> <span class="mf">1.1</span><span class="p">,</span> <span class="n">EggsAndSpam</span> <span class="mf">1.2</span><span class="p">,</span> <span class="n">EggsAndSpam</span> <span class="mf">1.3</span><span class="p">]</span>
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</pre></div>
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<p>We also could use version specifiers:</p>
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<div class="highlight"><pre><span class="o">>>></span> <span class="n">index</span><span class="o">.</span><span class="n">find</span><span class="p">(</span><span class="s">"EggsAndSpam (< =1.2)"</span><span class="p">)</span>
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<span class="p">[</span><span class="n">EggsAndSpam</span> <span class="mf">1.1</span><span class="p">,</span> <span class="n">EggsAndSpam</span> <span class="mf">1.2</span><span class="p">]</span>
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</pre></div>
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<p>Internally, what's done here is the following:</p>
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<ul class="simple">
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<li>it process the
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<a class="reference external" href="http://pypi.python.org/simple/FooBar/">http://pypi.python.org/simple/FooBar/</a>
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page, searching for download URLs.</li>
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<li>for each found distribution download URL, it creates an object,
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containing informations about the project name, the version and the
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URL where the archive remains.</li>
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<li>it sort the found distributions, using version numbers. The
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default behavior here is to prefer source distributions (over
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binary ones), and to rely on the last "final" distribution (rather
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than beta, alpha etc. ones)</li>
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</ul>
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<p>So, nothing hard or difficult here.</p>
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<p>We provides a bunch of other features, like relying on the new PyPI
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mirroring infrastructure or filter the found distributions by some
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criterias. If you're curious, please browse the
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<a class="reference external" href="http://distutils2.notmyidea.org/">distutils2 documentation</a>.</p>
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</div>
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<div class="section" id="using-xml-rpc">
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<h3>Using xml-rpc</h3>
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<p>We also can make some xmlrpc calls to retreive informations from
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PyPI. It's a really more reliable way to get informations from from
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the index (as it's just the index that provides the informations),
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but cost processes on the PyPI distant server.</p>
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<p>For now, this way of querying the xmlrpc client is not available on
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Distutils2, as I'm working on it. The main pieces are already
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present (I'll reuse some work I've made from the SimpleIndex
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querying, and
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<a class="reference external" href="http://github.com/ametaireau/pypiclient">some code already set up</a>),
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what I need to do is to provide a xml-rpc PyPI mock server, and
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that's on what I'm actually working on.</p>
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</div>
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</div>
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<div class="section" id="processes">
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<h2>Processes</h2>
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<p>For now, I'm trying to follow the "documentation, then test, then
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code" path, and that seems to be really needed while working with a
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community. Code is hard to read/understand, compared to
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documentation, and it's easier to change.</p>
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<p>While writing the simple index crawling work, I must have done this
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to avoid some changes on the API, and some loss of time.</p>
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<p>Also, I've set up
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<a class="reference external" href="http://wiki.notmyidea.org/distutils2_schedule">a schedule</a>, and
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the goal is to be sure everything will be ready in time, for the
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end of the summer. (And now, I need to learn to follow schedules
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...)</p>
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</div>
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