A virtualenv indicator that works everywhere

NOTE: While none of the significant elements of this approach require zsh, the formatting syntax and mechanism for updating a prompt dynamically differ between zsh and bash. See the end for a version with zsh-specific bits stripped out.

For a while, I’ve been using a variation on this zsh prompt tweak to get a pretty indication that I’m in a virtualenv. However, I was never quite satisfied with it for two reasons:

  1. It only works for virtualenvs activated through virtualenvwrapper
  2. It goes away if I launch a child shell… which is when I’m most likely to be confused and needing an indicator.

The solution was obvious: Instead of using a virtualenvwrapper hook, put something in my .zshrc which will detect virtualenvs opened through any means.

For those who just want something to copy-paste, here’s what I came up with:

zsh_virtualenv_prompt() {
    # If not in a virtualenv, print nothing
    [[ "$VIRTUAL_ENV" == "" ]] && return

    # Support both ~/.virtualenvs/<name> and <name>/venv
    local venv_name="${VIRTUAL_ENV##*/}"
    if [[ "$venv_name" == "venv" ]]; then

    # Distinguish between the shell where the virtualenv was activated and its
    # children
    if typeset -f deactivate >/dev/null; then
        echo "[%F{green}${venv_name}%f] "
        echo "<%F{green}${venv_name}%f> "


# Display a "we are in a virtualenv" indicator that works in child shells too

First, notice the use of VIRTUAL_ENV_DISABLE_PROMPT. This is because activate will prepend a less attractive indicator to PS1 that also goes away in child shells.

(Just make sure you remove any PS1="$_OLD_VIRTUAL_PS1" you might have added to postactivate or you’ll have no prompt after typing workon projname and be very confused.)

Second, note the use of PROMPT_SUBST. This is actually shared with my code for adding git branch information to PS1, PS2, and PS3 because profiling showed it to be faster than using a precmd function.

Third, note the single quotes for RPS1. That’s necessary to defer the invocation of $(check_virtualenv) so PROMPT_SUBST can see it.

I also added a couple of convenience features:

  • I have had a history of virtualenvwrapper not getting along with Python 3.x, so some of my projects have their virtualenvs at ~/src/<name>/venv rather than ~/.virtualenvs/<name>. This script will display <name> in the prompt either way.
  • If I’m in a child shell where the deactivate function isn’t available, the prompt will show <foo> rather than [foo] to make me aware of that.

Aside from that, it’s just ordinary efforts to avoid performing disk I/O or use $() in something that’s going to get run every time the prompt is displayed, and a function structured so the most common code path executes the fewest statements.

While this StackOverflow answer cautions against using VIRTUAL_ENV to detect virtualenvs, its reasoning doesn’t apply here, because it’s talking about detecting whether your Python script is running under the influence of a virtualenv, regardless of whether activate was used to achieve that. The purpose of this indicator, on the other hand, is specifically to detect the effects of activate so I don’t run something like manage.py runserver or pip install in the wrong context.

Bash Version

bash_virtualenv_prompt() {
    # If not in a virtualenv, print nothing
    [[ "$VIRTUAL_ENV" == "" ]] && return

    # Support both ~/.virtualenvs/<name> and <name>/venv
    local venv_name="${VIRTUAL_ENV##*/}"
    if [[ "$venv_name" == "venv" ]]; then

    # Distinguish between the shell where the virtualenv was activated and its
    # children
    if typeset -f deactivate >/dev/null; then
        echo "[${venv_name}] "
        echo "<${venv_name}> "

# Display a "we are in a virtualenv" indicator that works in child shells too

It’s almost identical to the zsh version, but the following functions which zsh provides for free are left to the reader in the bash version:

  • Implementing a right-aligned chunk of the prompt which stays properly positioned if you resize your terminal.
  • Using tput to retrieve the colour-setting escape sequences for your terminal and then caching them in a variable so you’re neither hard-coding for a specific terminal type nor performing multiple subprocess calls each time you display your prompt.

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How to skip the fortune command when your shell is slow to start

A.K.A. How to get and compare timestamps without external commands in shell script (and without even invoking subshells in Zsh)

I love the fortune command. It’s a charming little addition to each new tab I open… until something (like a nightly backup) has blown away my disk cache or a runaway memory leak is causing thrashing. Then, it’s just a big delay in getting to what I want to do.

The obvious solution to any non-shell programmer is to time everything and invoke fortune only if it’s not already taking too long, but shell script complicates that by having so few builtins. We don’t want to invoke an external process, because that would defeat the point of making fortune conditional, and we don’t want to invoke a subshell because, if we’re thrashing because of memory contention, that’ll also make things worse.

It turns out that bash 4.2 and above can get us half-way there by using a subshell to invoke the printf builtin with the %(%s)T token, but Zsh has a clever little solution that even reuses code that we’re going to need anyway: prompt substitutions!

Here’s the gist of how to pull it off:

# Top of .zshrc
local start_time="${(%):-"%D{%s}"}"

# -- Do all my .zshrc stuff here

local end_time="${(%):-"%D{%s}"}"
if [[ $(( end_time - start_time )) < 2 ]]; then
    if (( $+commands[fortune] )); then
    echo "Skipping fortune (slow startup)"

This is a standard “subtract start time from end time to get how long it took, then compare it to a threshold” check, so the only part that should need to be changed in bash is using start_time="$(printf "%(%s)T")". Instead, let’s pick apart how the Zsh version works:

  1. We start with a bog standard ${VAR:-DEFAULT} parameter expansion however, unlike bash, Zsh does consider ${:-always default} to be valid syntax.
  2. The (%) on the left-hand side is a special magic flag, similar to the (?i) syntax used for inline flag-setting in some regular expression engines. It enables prompt expansion of both the (nonexistent) variable’s contents and the fallback value.
  3. %D{...} is Zsh’s prompt expansion placeholder for putting strftime (man strftime(3)) timestamps into your prompt.
  4. %s is the strftime token for “seconds since the epoch”
  5. You have to quote the %D{...} or the ${...} consumes the closing curly brace too eagerly.

That’s the big magic thing. A way to write an equivalent to time(2) from the C standard library in pure Zsh script with no use of $(...) or zmodload and, since we’re using prompt expansion to do it, the only thing we might not already have needed to load into memory is the code for the %D{...} expansion token.

(Unfortunately, there’s no way to get sub-second precision with this approach, so the only two useful threshold values for a well-optimized zshrc are probably “1 second” and “2 seconds”.)

Now for that odd (( $+commands[fortune] )) way of checking for the presence of the fortune command. What’s up with that?

Well, it’s actually a micro-optimization that I use in my zsh-specific scripts. According to this guy’s tests, it runs in half the time the other options take and, in my own tests using his test scripts, I found that, depending on the circumstances, that could go as far as one tenth of the others, and that the others vary wildly relative to each other. (On runs where $+commands is 7 to 10 times as fast as type and which, hash is sometimes twice as fast as type or which and sometimes half as fast.)

Normally, this would be a moot point because any of the portable ways of checking for the existence of a command via a subshell and a builtin would be far too quick for it to matter (ie. I do it just for the heck of it) but, in this case, it felt appropriate.

(Another unnecessary micro-optimization that I didn’t use here was preferring [[ ]] over [ ] in my zshrc scripts. My tests found a million runs of [[ "$PWD" == "$HOME" ]] to take about 1.4 seconds, while a million runs of [ "$PWD" = "$HOME" ] took about 4.2 seconds.)

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On-Demand Loading for your .zshrc or .bashrc

Recently, I’ve been trying to make my coding environment snappier, and one thing I was never happy with was how slow my .zshrc is.

Now, don’t get me wrong, I’m not one of those people using oh-my-zsh with a ton of plugins and seeing 15-second waits for my shell to start… but I do want a new tab to be ready in a second or less.

So, I slapped zmodload zsh/zprof onto the top of my .zshrc, opened a new tab, and ran zprof | less …and 50% of the wait was in sourcing virtualenvwrapper, which I don’t feel like reinventing.

Time to take a lesson from the improvements I’ve been making to my .vimrc. Specifically, the { 'on': ['CommandA', 'CommandB'] } option hanging off the end of various lines for my plugin loader.

A little experimentation later and I came up with this construct:

function init_virtualenvwrapper {
    # Don't do anything if it's already loaded
    type virtualenvwrapper_workon_help &>/dev/null && return

    # ------------------------------------------------
    # normal stuff to load virtualenvwrapper goes here
    # ------------------------------------------------

for cmd in workon mkproject mkvirtualenv; do
    function $cmd {
        unset -f "$0"
        "$0" "$@"

For those not familiar with shell scripting, I’ll clarify.

For each shell function or command that I want to trigger deferred loading, I create a function with the same name that does the following:

  1. “Delete” itself so it won’t interfere with what virtualenvwrapper is going to set up. (You want to do this first to avoid removing what virtualenvwrapper just created)
  2. Call the virtualenvwrapper setup code to load the real command.
  3. init_virtualenvwrapper starts by checking for some side-effect of having been run before and exits early if that’s the case. (This keeps mkproject from re-doing what workon already did, or vice-versa.)
  4. Call the actual command and pass through any arguments.

Doing this means that:

  1. Your .zshrc or .bashrc startup time only pays the price for declaring a few shell functions. (And, if that gets too heavy for some reason, you could move init_virtualenvwrapper into another file and source it on demand.)
  2. Your first call to a wrapped command like workon will take longer. (eg. if it was adding two seconds to your shell start time, then your first call to it will take two seconds longer.)
  3. Subsequent calls to that or any other command sharing the same init_virtualenvwrapper will be as quick as usual.

Unfortunately, this design is actually Zsh-specific, which sucks for me because this is a file I share between .zshrc and .bashrc:

  1. Bash doesn’t support using a variable for a function name, so you can’t use a for loop. You’ll just get `$cmd': not a valid identifier.
  2. In my testing, functions didn’t set $0 in bash, so this will actually execute bash "$@", bringing you back to where you started, while zsh doesn’t set the FUNCNAME array variable that bash uses.

So, if you want to support both, here’s the most concise form I was able to put together:

function init_virtualenvwrapper {
    local _cmdname="$1"
    unset -f "$_cmdname"

    # Don't do anything if it's already loaded
    if ! type virtualenvwrapper_workon_help &>/dev/null; then
            # ----------------------------------------
            # normal stuff to load virtualenvwrapper
            # ----------------------------------------

    "$_cmdname" "$@"
# }}}

function workon {
    init_virtualenvwrapper "${FUNCNAME[0]:-$0}" "$@"
function mkproject {
    init_virtualenvwrapper "${FUNCNAME[0]:-$0}" "$@"
function mkvirtualenv {
    init_virtualenvwrapper "${FUNCNAME[0]:-$0}" "$@"

Anyway, I hope this helps to inspire anyone else who’s suffering from slow shell startup times.

UPDATE: And now, shortly after writing that, I discover that someone else went to the trouble of using eval to provide a nice API on top of this trick and put it up on GitHub as sandboxd. From that name, I can see why i didn’t find it before.

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So… What Does Your Government Do With Culture?

So often, asking people about culture is like asking a fish “How’s the water?” (The answer you’ll get is “What’s water?”) but it’s still useful to ask the question and, sometimes, you get interesting answers.

This time I’m wondering about ways your country’s government promoted the enrichment of culture and I think the best way to jog people’s memories is to give a bunch of examples of the kind of thing I’m talking about.

Everyone’s at least heard of government grant programs in the abstract (and Canada does have those. They’ve been instrumental in the creation of indie games I love, like Guacamelee, and shows like Mayday, a long-running docudrama series nominated for many awards which, unlike so many American ones, remembers that air crash investigations are detective stories first and human drama second)

Can you think of any “thanks to” credits for other government agencies or programs that show up in the credits of your favourite shows or on the websites of your favourite games?

…but, still, that’s kind of an obvious way to do it. What about stuff that’s less overtly “government promoting culture”?

Next down the progression of obviousness, there’s public broadcasting. Like the U.K., Canada has a public broadcaster (the CBC). It does produce excellent content of its own, such as the radio programs Quirks & Quarks and Because News (also available as podcasts), and it has adapted well to the Internet era (in addition to podcasts and the like, they also do print articles now), but it was actually ahead of its time. For quite a while before YouTube came around, you used to be able to watch complete archives of shows like Royal Canadian Air Farce on the CBC website in RealVideo format.

The U.K. actually has more than one public broadcaster. For everyone who knows about the BBC, how many of you know that Channel 4 (of Time Team fame) is also government-owned?

… but encountering your public broadcaster while channel-surfing is still too obvious. Let’s go deeper.

For example, since 1961, the CBC has been part of a partnership with House of Anansi Press and the University of Toronto to produce the Massey Lectures. If you like TED Talks, check them out. (I especially recommend Doris Lessing’s Prisons We Choose To Live Inside from 1985. It’s an amazing talk about human psychology that’s more relevant than ever, you can listen to it online for free, and, to my embarrassment, I didn’t know about it until the print version was assigned to me as reading in university.)

Can you think of anything your government contributes resources to along these lines? Recurring cultural events?

…how about PSAs that go beyond just being practical and help to spread culture? When I was a child, I don’t remember CBC television having commercials… though it’s possible they just had a reduced supply of them. The important thing is, their shows were formatted to leave room for a normal number of commercials. …so how did they fill that time?

Some other channels, such as the Family Channel (a kids channel which used to be commercial-free), filled the time with random pop music videos, but CBC did something a little more appropriate… they filled the time with shorts provided by other government-backed cultural enterprises like the National Film Board of Canada, and Canadian Heritage Minutes. Anyone who grew up in Canada is likely to fondly remember these things, so I’d say it was hugely effective.

Like so many kids, I forgot most of what I learned in history class, but I still remember about the amusing origin of the name Canada, the Halifax explosion, and the origin of Winnie the Pooh.

Likewise, what kid would know about Wade Hemsworth’s music if not for classic animated shorts like The Log Driver’s Waltz and The Blackfly Song produced by The National Film Board of Canada? (Not to mention the classic cartoon version of The Cat Came Back?)

Can you think of anything this engaging that your government actively produced or did they stick to purely functional pieces like Duck and Cover? (I’ll also accept stuff that isn’t distinctive to your local culture, but demonstrates that PSAs can be entertainment in their own right, such as Australia’s Dumb Ways to Die.)

Anyway, now we get to the stuff you take most for granted.

When I was a kid and I occasionally saw American money, I’d think “Huh. American money is ugly.” Much later, my father brought home a bunch of European coins. To my surprise, it turns out that it’s not that American money is ugly… it’s that Canadian money is uncommonly artistic. Of all the money I saw, the only other country with comparably beautiful coinage was Ireland. Don’t believe me? Scroll down to the pictures on these pages. (Note: I linked to pre-Euro Irish currency because that’s what I saw.)

The U.S., the U.K., Belgium, France, Switzerland, Germany… every other coin I saw had some boring piece of patriotic imagery or maybe a coat of arms, while Canadian and Irish coins were beautiful expressions of the culture of the nation in question. (Don’t believe me? Here’s the Canadian 50 dollar bill from 2004… that imagery commemorating The Famous Five wasn’t a special commemorative bill. That was the normal fifty.)

It makes it look as if all those cultures have deep insecurities, so they’re “compensating for something” with their patriotic imagery. It’s such a given that I love my country that, for most of my life, I never understood the point of putting up a Canadian flag on a non-government property. Why plaster the same patriotic imagery everywhere like graffiti when you can instead be expressing yourself, either by creating your own art or by displaying other people’s art which speaks to your sense of aesthetics.

…but enough of that tangent. Another example would be the Canadian flag. No tiny details like on Mexico’s flag, but still with more artistry recognizable to the common person than all those flags made of coloured rectangles and/or stars. (I’m not singling the U.S. out here. Look at France, the U.K., Russia, and countless other countries.)

It just seems like counties get boring when the topic of government art comes around. The only other flags that readily come to mind as having that kind of elegance are the Japanese and South Korean flags and the fern iconography that showed up in the New Zealand flag referendums.

…or, for that matter, look at the elegance of the T-130 wordmark [2] used on official Canadian government documents and signage, such as equally elegant T-605 primary identification signs.)

If you’re going to see something in so many places, why is it such a rare idea for government decision makers to grasp that it should be as aesthetically satisfying as possible?

It took me years to notice these things, so I’m really curious to see examples where Canada is the boring one and I’m just taking it for granted that thing X and thing Y are boring. (Does anyone have a really interesting national anthem? Canada’s seems to be just as boring as the American and Australian ones.)

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Forcing Firefox to Open CBZ Files Properly

If you’ve ever downloaded a .cbz file using Firefox and then tried to click it in the downloads panel, you might have noticed that Firefox ignores the association for the .cbz extension and instead opens it as a .zip file. (This isn’t the only situation where this happens and I filed a bug about it a year ago.)

I never got around to looking into why it doesn’t make the same mistake with .odt documents, which are also Zip files with a specialized extension, but I think you can see why I wouldn’t like it.

Here’s a quick little script that can be set as the Zip handler on a KDE-based desktop which will hand over to Ark under normal circumstances but, if it receives a file with a .cbz extension, will pop up a Yes/No dialog offering to open in Comix instead.

Anything which obeys the system’s associations properly will never trigger it, because .cbz files will be associated with Comix and it won’t pop up the dialog if fed a .zip file, so it’s about the best solution one can have without fixing Firefox.

This approach could also be easily extended to application/octet-stream to work around the other situation where I’ve seen this causing problems. (Patreon serving up image files with the wrong mimetype, if I remember correctly.)

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Displaying An Image or Animated GIF in Qt With Aspect Ratio-Preserving Scaling

When it comes to me and organizing images, GQView (now Geeqie) has always been a “best of a bunch of bad options” sort of thing and, with my move off Kubuntu 14.04 LTS, it’s become downright unusable in some cases. (eg. Freezing up at 100% CPU for several minutes to load certain collections)

As a result, I’ve been pushed to prioritize my efforts to replace at least the bare minimum subset of that functionality and, since I don’t want to rely on gtk3-mushrooms to make my own creations tolerable to me and Rust doesn’t have mature Qt bindings, that means PyQt5.

It’s not perfect (Qt doesn’t have incremental loading like GdkPixbufLoader, so I have to rely more heavily on my prototype code for asynchronously loading a bunch of upcoming images ahead in the background while I dawdle looking at the current one) but it’ll have to do… and I’ve filed a bug about that.

Now Qt has always been weird about how to get a displayed image to preserve its aspect ratio properly. It’s probably the one really glaring oversight in an otherwise very nicely designed and documented set of APIs. Given how much I had to fiddle around with things, I decided that I definitely wanted to share what I came up with.

What made it more difficult is that I’ve always wanted a GQView-alike which also displays animated GIFs with their animation, and Qt doesn’t have a unified solution for that. (QImage handles static images and QMovie handles GIF and MNG, but not actual movies, which you need to use the multimedia backend for.)

It turns out that getting smooth upscaling with QMovie is a tricky thing in itself because it’s very easy to accidentally build a widget tree that does the upscaling at a point in the pipeline where fast/ugly upscaling gets used, so a big thanks to Spencer on StackOverflow who figured it out.

Anyway, enough talk. Here’s the code:

(Yeah. I was too eager to post it, so this prototype hasn’t actually been split into the design which allows me to put the cache after the images get decoded. Still, it should be useful for most people.)

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On Dehumanization In Fiction

I have to admit it… I have a lot of drafts kicking around in my notes which most people would consider to be perfectly good blog posts but which, for me, were just flashes of inspiration that I wrote down to avoid losing them, but I never felt were “finished”.

While I was looking through the snips I’m accumulating for a book on writing, I rediscovered a couple which, looking at them now, are good enough to share, even if I still feel that there’s more insight to be teased out and more room for the style to be polished.

Dehumanization is at the heart of some of the most effective dark writing.

What hits harder than cruelty? Casual cruelty.
What hits harder than casual cruelty? Institutionalized cruelty.

Dropping a man in the wilderness, hundreds of miles from the nearest human, will cause hardship, but, if you want a man to despair, drop him into the heart of a big city, penniless, alone, and ignored by all who pass… and that’s just from cruelty by neglect.

Humans are social animals to our very core, and slavery is abhorrent precisely because its institutionalized cruelty at its most powerful… forcing the reader to not only observe active dehumanization on a mass scale, but to confront how flawed their optimistic preconceptions of human nature are in a way that rings too true for them to deny.

(Humanity’s social nature is also why solitary confinement is considered torture in many places, but this is much more difficult to communicate to someone who hasn’t experienced it personally.)

Looking at it from another angle, it’s also so powerful because of the specific kinds of emotions it evokes in the reader/viewer via their sense of empathy. It’s not just that the character is experiencing misery or defeat or isolation, it’s that their circumstances evoke a sense of despair AND powerlessness, futility AND hopelessness.

Most telling, I think, is how Chip Conley pseudo-mathematically expressed despair: suffering without meaning… and isn’t that also the perfect starting point for a definition of my own term, “Hardship Porn”. (Fiction where, through intent or incompetence, the author seems to revel in making their hero’s life miserable, not because it makes the writing more powerful but just to gratify some emotional need.)

I also made a related observation that slavery is powerful because it tends to associate itself well to two kinds of atrocities which fall under the other major class of violations we readily recognize: the sanctity of self.

To wilfully and permanently disfigure someone’s body against their desires, or to attack their very psyche, is the most personal form of dehumanization possible… denying you control over the only things that are unarguably, undeniably, unquestionably your own and attacking your thoughts, the one hiding place nobody should ever intrude… let alone tamper with. It is no accident that, as a species who think in metaphor, we often refer to the body as a temple and the mind as a sanctum.

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