Here's a common Python idiom that is broken on macOS 10.13 and beyond:
import os, requests
pid = os.fork()
if pid == 0:
# I am the child process.
# I am the parent process.
Now, it's important to stress that this particular code sample may execute
just fine. It's an excerpt from some code at work that illustrates a deeper
problem that you may or may not encounter in real-world applications. We've
seen it crash reproducibly, resulting in core dumps of the Python process,
with potentially disk filling dump files in /cores.
In this article, I hope to explain what I know about this problem, with links
to information elsewhere on the 'net. Some of those resources include
workarounds, but in my experiments, those are not completely reliable in
eliminating the core dumps. I'll explain why I think that is.
It's important to stress that at the time of this article's publishing, I do
not have a complete solution, and am not even sure one exists. I'll note
further that this is not specifically a Python problem and in fact has been
described within the Ruby community. It is endemic to common idioms around
the use of fork() without exec*() in scripting languages, and is caused
by changes in the Objective-C runtime in macOS 10.13 High Sierra and
beyond. It can also be observed in certain "prefork" servers.
What is forking?
I won't go into much detail on this, since any POSIX programmer should be well
acquainted with the fork(2) system call, and besides, there are tons of
other good resources on the 'net that explain fork(). For our purposes
here, it's enough to know that fork() is a relatively inexpensive way to
make an exact copy of …
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I turn my back to the wind
To catch my breath,
Before I start off again
-- Neil Peart, Time Stand Still
23 years ago, I met Guido, fell in love with Python, and took a turn that
changed the course of my life and career. You can't ever know where your
decisions will lead you, so you just have to set a course and trust the wind.
In the 1990s, as we moved the Python.Org infrastructure from the Netherlands
to the US, we inherited the Majordomo list server that was running
firstname.lastname@example.org. There were changes we wanted to make and features
we wanted to add, but it was becoming increasingly clear that Majordomo had to
be replaced. Besides being difficult to hack on, it was written in Perl, so
of course that wouldn't do at all. Python was an upstart disrupting its
space, and we needed a list server written in Python that was malleable enough
for us to express our ideas.
It was about that time that our friend John Viega showed us a project he'd
been working on. He'd wanted to connect a popular, local Charlottesville,
Virginia band with their fans at UVA, and email lists were an important way to
do that. Of course, no one wants to manage such lists manually, and if you're
not happy with the existing options, what does any self-respecting developer
do? You write yourself a new one! As for implementation language, was there
really any other choice? History celebrates this momentous confluence of
events: the band became the mega-rock powerhouse known as the Dave Matthews
Band, and the mailing list software John wrote is what became GNU Mailman.
(Aside: I'll never forget the time my band the Cravin' Dogs played at TRAX,
a Charlottesville music venue. The place …
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Written by Barry Warsaw in music on Sun 05 March 2017. Tags: music,
Although I've been signed up for 8 years, 2017 is the first time I've
completed the RPM Challenge. The challenge is deceptively simple: record
an album in February that's 10 songs or 35 minutes long. All the material
must be previously unreleased, and it's encouraged to write the music in
The second question of the FAQ is key: "Is it cheating...?" and the answer is
"Why are you asking?".
RPM is not a contest. There are no winners (except for everyone who loves
music) and no prizes. I viewed it as a personal creative challenge, and it
certainly was that! As the days wound down, I had 9 songs that I liked, but I
was struggling with number 10. I was also about 4 minutes short. I'd
recorded a bunch of ideas that weren't panning out, and then on the last
Saturday of February, I happened to be free from gigs and other commitments.
Yet I was kind of dreading staring at an empty project (the modern musician's
proverbial empty page), when one of my best friends in the world, Torro Gamble
called me up and asked what I was doing. Torro's a great drummer (and guitar
player, and bass player...) so he came over and we laid down a bunch of very
cool ideas. One of them was perfect for song number 10.
The great thing about this challenge is the deadline. When you have a home
studio, there's little to stop you from obsessing about every little detail.
I can't tell you how many mixes I made, tweaking the vocals up a bit, then
bringing them back down. Or adding a little guitar embellishment only to bury
it later. And you don't even want to look at the comps of the dozens of bass
and vocal …
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I'm always going to remember January 20, 2017 as a beautiful day.
Those who know me, and know the significance of that date, will no doubt
wonder if I've lost my mind. But let me explain why a day that could have
been filled with crushing physical and psychic depression, instead is not only
filled with light and love, but I think planted the seeds for what must
inevitably come next.
I'm writing this in a sort of quantum superposition. I haven't read or heard
any news since about 8pm last night. My wife and son are down at the Women's
March in Washington DC and I've woken late, had breakfast, done my morning tai
chi and meditation, and now I sit down to try to put some of my thoughts onto
You probably know what else happened on that date. And if so, the question
is: why was last night so revitalizing, so positive? Because a trio of
U-Liners played an enthusiastic set as one act in a night of three, filled
with transcendent music and amazingly bright joyful people.
I'd thought the gig was going to be a night of protest against a new,
unthinkable political reality, and the message of hate and fear that came
along with it. But it wasn't a protest gig, it was a celebration.
The show was at Gypsy Sally's, a club with a great vibe down in Washington
DC's Georgetown area, under the Whitehurst Freeway. I've played there several
times with several different groups, including my main bands the Cravin'
Dogs and the U-Liners. Some places (musical and otherwise), just have a
Vibe. You can tell that magic happens there. The Barn at Keuka Lake where
I've attended tai chi camp has that vibe. All the hours and hours of
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For a project at work we create sparse files, which on Linux and other
POSIX systems, represent empty blocks more efficiently. Let's say you have a
file that's a gibibyte in size, but which contains mostly zeros,
i.e. the NUL byte. It would be inefficient to write out all those zeros, so
file systems that support sparse files actually just write some metadata to
represent all those zeros. The real, non-zero data is then written wherever
it may occur. These sections of zero bytes are called "holes".
Sparse files are used in many situations, such as disk images, database files,
etc. so having an efficient representation is pretty important. When the file
is read, the operating system transparently turns those holes into the correct
number of zero bytes, so software reading sparse files generally don't have to
do anything special. They just read data as normal, and the OS gives them
zeros for the holes.
You can create a sparse file right from the shell:
$ truncate -s 1000000 /tmp/sparse
Now /tmp/sparse is a file containing one million zeros. It actually
consumes almost no space on disk (just some metadata), but for most intents
and purposes, the file is one million bytes in size:
$ ls -l /tmp/sparse
-rw-rw-r-- 1 barry barry 1000000 Jan 14 11:36 /tmp/sparse
$ wc -c /tmp/sparse
The commands ls and wc don't really know or care that the file is
sparse; they just keep working as if it weren't.
But, sometimes you do need to know that a file contains holes. A common
case is if you want to copy the file to some other location, say on a
different file system. A naive use of cp will fill in those holes, so a
command like this …
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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
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
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
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 and use that
as a new repository URL. This won't be …
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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.
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 for their land and environment, as
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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
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!
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 lightweight and easy,
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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
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
other kinds of resources. I won't go …
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