Building Debian packages with local dependencies

Written by Barry Warsaw in technology on Mon 28 November 2016. Tags: ubuntu, debian, packaging,

Way back in 2011 I wrote an article describing how you can build Debian packages with local dependencies for testing purposes. An example would be a new version of a package that has new dependencies. Or perhaps the new dependency isn't available in Debian yet. You'd like to test both packages together locally before uploading. Using sbuild and autopkgtest you can have a high degree of confidence about the quality of your packages before you upload them.

Here I'll describe some of the improvements in those tools, and give you simplified instructions on how to build and test packages with local dependencies.

What's changed?

Several things have changed. Probably the biggest thing that simplifies the procedure is that GPG keys for your local repository are no longer needed.

Another thing that's improved is the package testing support. It used to be that packages could only be tested during build time, but with the addition of the autopkgtest tool, we can also test the built packages under various scenarios. This is important because it more closely mimics what your package's users will see. One thing that's cool about this for Python packages is that autopkgtest runs an import test of your package by default, so even if you don't add any explicit tests, you still get something. Of course, if you do want to add your own tests, you'll need to recreate those default tests, or check out the autodep8 package for some helpers.

I've moved the repository of scripts over to git.

The way you specify the location of the extra repositories holding your local debs has changed. Now, instead of providing a directory on the local file system, we're going to fire up a simple Python-based HTTP server ...

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Kiwi PyCon 2016, Pt I

Written by Barry Warsaw in technology on Mon 19 September 2016. Tags: python, travel,

In early September 2016 I traveled to New Zealand to give a keynote speech for Kiwi PyCon 2016. I was very honored to be invited, and glad that after 4 years of valiant resistance, I finally gave in to my thankfully diligent colleague Thomi Richards. My wife Jane and I made the 25+ hour journey, and had a wonderful little vacation after the conference.

Here in part I, I'll talk a bit about the conference and my keynote. Later in part II, I'll talk about the vacation part of the trip. I might sprinkle little impressions of New Zealand throughout both articles.

Getting there

In some ways, it's a good thing that New Zealand is so far from the USA, with an additional transcontinental trip away from the east coast. During our summer, it's their winter and they are 16 hours ahead of UTC-4. Meaning that at noon New York time, it's 4am the next day in New Zealand. Or, to put it another way, 8am New Zealand time is 4pm New York time the previous day. I never got tired of the joke with family back home that we were living in the future over there.

So it's definitely a commitment to get there, which makes it all the more breathtaking I think. In a way, New Zealand feels exotic because the first thing that most Americans probably think of when they hear "New Zealand" is the "Lord of the Rings" movies. But New Zealand is a high-tech country, with a low population (under 5 million people in total) concentrated in four major cities (Auckland, Christchurch, Dunedin, and Wellington), lots of sheep and some of the nicest people you'll meet in the English speaking world. They have a real sense of stewardship ...

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We Fear Change returns

Written by Barry Warsaw in technology on Mon 25 April 2016. Tags: blogging,

I'm back! This time, I'm using the very awesome Pelican publishing platform, as Blogger just got to be too much of a pain to use. Let's hope that the simplicity of using reStructuredText, static pages, and outsourcing discussions will make it so easy to blog that I actually keep doing it. I've slapped together a basic theme, but no doubt I'll be tweaking it as time goes on. For now, the theme isn't in a public repository. A quick shout out to Font Awesome and font-linux for their very cool font icons.

I do intend to expand the themes I blog about. I'll still focus on Python and GNU Mailman as well as other technology, but now I'll include tai chi, music, and anything else that I feel the overwhelming urge to share. I hope I can continue to present my thoughts in a respectful, positive, all-inclusive voice.

I've migrated most of the pages from the old Blogger platform, and done some minor updating as appropriate. One of the main reasons I've moved off of Blogger was because of the pain of moderating comments. There was just too much spam. I've switched to the third party discussion platform Disqus and I've tried to import all the non-spammy original comments. I'm not sure I've done that correctly, but we'll see!

You can contact me via the Social links in the side bar, and via the various public mailing lists and IRC channels I hang out in. I hope to hear from you!


Creating Python snaps

Written by Barry Warsaw in technology on Thu 02 April 2015. Tags: debugging, python, python3, ubuntu,

Background

Snappy Ubuntu Core is a new edition of the Ubuntu you know and love, with some interesting new features, including atomic, transactional updates, and a much more lightweight application deployment story than traditional Debian/Ubuntu packaging. Much of this work grew out of our development of a mobile/touch based version of Ubuntu for phones and tablets, but now Ubuntu Core is available for clouds and devices.

I find the transactional nature of upgrades to be very interesting. While you still get a perfectly normal Ubuntu system, your root file system is read-only, so traditional apt-get based upgrades don't work. Instead, your system version is image based; today you are running image 231 and tomorrow a new image is released to get you to 232. When you upgrade to the new image, you get all the system changes. We support both full and delta upgrades (the latter which reduces bandwidth), and even phased updates so that we can roll out new upgrades and quickly pull them from the server side if we notice a problem. Snappy devices even support rolling back upgrades on a single device, by using a dual-partition root file system. Phones generally don't support this due to lack of available space on the device.

Of course, the other part really interesting thing about Snappy is the lightweight, flexible approach to deploying applications. I still remember my early days learning how to package software for Debian and Ubuntu, and now that I'm both an Ubuntu Core Developer and Debian Developer, I understand pretty well how to properly package things. There's still plenty of black art involved, even for relatively easy upstream packages such as distutils/setuptools-based Python packages available on the Cheeseshop (er, PyPI). The Snappy approach on Ubuntu Core is much more ...

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Resource management in Python 3.3, or contextlib.ExitStack FTW!

Written by Barry Warsaw in technology on Fri 10 May 2013. Tags: python, python3, ubuntu,

I'm writing a bunch of new code these days for Ubuntu Touch's Image Based Upgrade_ system. Think of it essentially as Ubuntu Touch's version of upgrading the phone/tablet (affectionately called *phablet*) operating system in a bulk way rather than piecemeal `apt-get s the way you do it on a traditional Ubuntu desktop or server. One of the key differences is that a phone has to detour through a reboot in order to apply an upgrade since its Ubuntu root file system is mounted read-only during the user session.

Anyway, those details aren't the focus of this article. Instead, just realize that because it's a pile of new code, and because we want to rid ourselves of Python 2, at least on the phablet image if not everywhere else in Ubuntu, I am prototyping all this in Python 3, and specifically 3.3. This means that I can use all the latest and greatest cool stuff in the most recent stable Python release. And man, is there a lot of cool stuff!

One module in particular that I'm especially fond of is contextlib. Context managers are objects implementing the protocol behind the with statement, and they are typically used to guarantee that some resource is cleaned up properly, even in the event of error conditions. When you see code like this:

with open(somefile) as fp:
    data = fp.read()

you are invoking a context manager. Python was clever enough to make file objects support the context manager protocol so that you never have to explicitly close the file; that happens automatically when the with statement completes, regardless of whether the code inside the with statement succeeds or raises an exception.

It's also very easy to define your own context managers to properly handle ...

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Python 3 Language Gotcha -- and a short reminisce

Written by Barry Warsaw in technology on Thu 18 April 2013. Tags: python, python3, ubuntu,

There's a lot of Python nostalgia going around today, from Brett Cannon's 10 year anniversary of becoming a core developer, to Guido reminding us that he came to the USA 18 years ago. Despite my stolen time machine keys, I don't want to dwell in the past, except to say that I echo much of what Brett says. I had no idea how life changing it would be -- on both a personal and professional level -- when Roger Masse and I met Guido at NIST at the first Python workshop back in November 1994. The lyric goes: what a long strange trip it's been, and that's for sure. There were about 20 people at that first workshop, and 2500 at Pycon 2013.

And Python continues to hold little surprises. Just today, I solved a bug in an Ubuntu package that's been perplexing us for weeks. I'd looked at the code dozens of times and saw nothing wrong. I even knew about the underlying corner of the language, but didn't put them together until just now. Here's a boiled down example, see if you can spot the bug!

import sys

def bar(i):
    if i == 1:
        raise KeyError(1)
    if i == 2:
        raise ValueError(2)


def bad():
    e = None
    try:
        bar(int(sys.argv[1]))
    except KeyError as e:
        print('ke')
    except ValueError as e:
        print('ve')
    print(e)

bad()

Here's a hint: this works under Python 2, but gives you an UnboundLocalError on the e variable under Python 3.

Why?

The reason is that in Python 3, the targets of except clauses are del'd from the current namespace after the try...except clause executes. This is to prevent circular references that occur when the exception is bound to the target ...

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UDS Update #1 - OAuth

Written by Barry Warsaw in technology on Wed 21 November 2012. Tags: debian, python, python3, ubuntu, uds-r,

For UDS-R for Raring (i.e. Ubuntu 13.04) in Copenhagen, I sponsored three blueprints. These blueprints represent most of the work I will be doing for the next 6 months, as we're well on our way to the next LTS, Ubuntu 14.04.

I'll provide some updates to the other blueprints later, but for now, I want to talk about OAuth and Python 3. OAuth is a protocol which allows you to programmatically interact with certain website APIs, in an authenticated manner, without having to provide your website password. Essentially, it allows you to generate an authorization token which you can use instead, and it allows you to manage and share these tokens with applications, so that you can revoke them if you want, or decide how and which applications to trust to act on your behalf.

A good example of a site that uses OAuth is Launchpad, but many other sites also support OAuth, such as Twitter and Facebook.

There are actually two versions of OAuth out there. OAuth version 1 is definitely the more prevalent, since it has been around for years, is relatively simple (at least on the client side), and enshrined in RFC 5849. There are tons of libraries available that support OAuth v1, in a multitude of languages, with Python being no exception.

OAuth v2 is much less common, since it is currently only a draft specification, and has had its share of design-by-committee controversy. Still, some sites such as Facebook do require OAuth v2.

One of the very earliest Python libraries to support OAuth v1, on both the client and server side, was python-oauth (I'll use the Debian package names in this post), and on the Ubuntu desktop, you'll find lots of scripts and libraries that use python-oauth. There ...

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The right way to internationalize your Python app

Written by Barry Warsaw in technology on Fri 22 June 2012. Tags: i18n, mailman, python, python3, ubuntu,

Recently, as part of our push to ship only Python 3 on the Ubuntu 12.10 desktop, I've helped several projects update their internationalization (i18n) support. I've seen lots of instances of suboptimal Python 2 i18n code, which leads to liberal sprinkling of cargo culted .decode() and .encode() calls simply to avoid the dreaded UnicodeError s. These get worse when the application or library is ported to Python 3 because then even the workarounds aren't enough to prevent nasty failures in non-ASCII environments (i.e. the non-English speaking world majority :).

Let's be honest though, the problem is not because these developers are crappy coders! In fact, far from it, the folks I've talked with are really really smart, experienced Pythonistas. The fundamental problem is Python 2's 8-bit string type which doubles as a bytes type, and the terrible API of the built-in Python 2 gettext module, which does its utmost to sabotage your Python 2 i18n programs. I take considerable blame for the latter, since I wrote the original version of that module. At the time, I really didn't understand unicodes (this is probably also evident in the mess I made of the email package). Oh, to really have access to Guido's time machine.

The good news is that we now know how to do i18n right, especially in a bilingual Python 2/3 world, and the Python 3 gettext module fixes the most egregious problems in the Python 2 version. Hopefully this article does some measure of making up for my past sins.

Stop right here and go watch Ned Batchelder's talk from PyCon 2012 entitled Pragmatic Unicode, or How Do I Stop the Pain? It's the single best description of the background and effective use of Unicode in ...

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Python 3 on the desktop for Quantal Quetzal

Written by Barry Warsaw in technology on Tue 24 April 2012. Tags: canonical, debian, ubuntu, python, python3,

So, now all the world now knows that my suggested code name for Ubuntu 12.10, Qwazy Quahog, was not chosen by Mark. Oh well, maybe I'll have more luck with Racy Roadrunner.

In any case, Ubuntu 12.04 LTS is to be released any day now so it's time for my semi-annual report on Python plans for Ubuntu. I seem to write about this every cycle, so 12.10 is no exception. We've made some fantastic progress, but now it's time to get serious.

For Ubuntu 12.10, we've made it a release goal to have Python 3 only on the desktop CD images. The usual caveats apply: Python 2.7 isn't going away; it will still probably always be available in the main archive. This release goal also doesn't affect other installation CD images, such as server, or other Ubuntu flavors. The relatively modest goal then only affects packages for the standard desktop CD images, i.e. the alternative installation CD and the live CD.

Update 2012-04-25: To be crystal clear, if you depend on Python 2.7, the only thing that changes for you is that after a fresh install from the desktop CD on a new machine, you'll have to explicitly apt-get install *python2.7. After that, everything else will be the same.

This is ostensibly an effort to port a significant chunk of Ubuntu to Python 3, but it really is a much wider, Python-community driven effort. Ubuntu has its priorities, but I personally want to see a world where Python 3 rules the day, and we can finally start scoffing at Python 2 :).

Still, that leaves us with about 145 binary packages (and many fewer source packages) to port. There are a few categories of packages ...

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Debian packaging for Python 2 and 3

Written by Barry Warsaw in technology on Wed 18 January 2012. Tags: python, debian,

Time for another installment of my ongoing mission to convert the world to Python 3! This time, a little Debian packaging-fu for modifying an existing Python 2 package to include support for Python 3 from the same source package.

Today, I added a python3-feedparser package to Ubuntu Precise. What's interesting about this is that, despite various reported problems, upstream feedparser 5.1 claims to support Python 3, via 2to3 conversion. And indeed it does (although the test suite does not).

Before today, Ubuntu had feedparser 5.0.1 in its archive, and while some work has been done to update the Debian package to 5.1, this has not been released. The uninteresting precursor to Python 3 packaging was to upgrade the Ubuntu version of the python-feedparser source package to 5.1. I'll spare you the boring details about missing data files in the upstream tarball, and other problems, since they don't really relate to the Python 3 effort.

The first step was to verify that feedparser 5.1 works with Python 3.2 in a virtualenv, and indeed it does. This is good news because it means that the setup.py does the right thing, which is always the best way to start supporting Python 3. I've found that it's much easier to build a solid Debian package if you have a solid setup.py in upstream to begin with.

Now, what I'd like to do is to give you a recipe for modifying your existing debian/ directory files to add Python 3 support to a package that already exists for Python 2. This is a little trickier for feedparser because it used an older debhelper standard, and carried some crufty old stuff in its rules file. My first step was to update ...

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