Category Archives: Programming

Notes from Cleveland code retreat

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I attended the day-long Code Retreat at Lean Dog’s floating office on Sunday.

We worked in pairs for 45-minute blocks of time, building Conway’s Game of Life. In each session, we started from the beginning. We didn’t build on previous code.

After each session, teams talked about what stuff they discovered. Then we reorganized into new pairs and started working from the beginning again.

First pairing

At first I paired with a C# developer. While other teams went right into writing test programs, we spent a fair amount of time talking and sketching out ideas about how to model the game.

Then we made a grid that knew how to generate the next state just by copying itself into a new grid.

We planned to add in code to support each of the four rules of the game of life one by one.

So, we wrote a test that created a grid with just a single living cell. Then we told that grid to make a grid for the next generation, and our test verified that the single cell survived the copy.

Then we started working on the first rule: if a cell is alive and has less than two neighbors, it dies.

We burned through the reminder of time sketching out ideas on my clipboard. By the end of our time, it was clear that we only needed to pay attention to living cells and neighbors of living cells.

It was also clear that the time spent writing the first test and then writing the code to satisfy the first test did nothing to move us toward a real solution.

Second pairing

Next I worked with a Java guy. This time, we did something a little closer to TDD.

We decided to start from the point of view of an end-user firing up the game. The user would want to make a grid, add a few living cells, and then tell the grid to generate its next state.

The first code we wrote was a test and we started writing tests almost immediately. In the test, we instantiated a Grid class. That test blew up with an error, since no Grid class existed. So then we wrote a grid class. It had no methods or attributes, but that was all we needed to write in order to satisfy our test.

Next we wrote a new test that instantiated a grid and then added a single cell by calling an (undefined) addCell(…) method.

After seeing that test crash with an error, we wrote an addCell(…) method that was a no-op, because that’s all our tests required us to do.

Then we wrote a test for rule one, where a living cell with less than two neighbors dies.

In this test, we made a grid, added a single cell, and then told the grid to create a new grid that represented itself in the future. Then we used an assert to verify the new grid had no cells.

First we added a “cells” instance-level ListArray attribute to our grid class. Then we wrote a generate_next_grid method on our grid class, and all that did was instantiate and return a new grid with an empty cells.

And bingo, we had enough code again to pass our test.

At this point, I became convinced that the kind of testing we were doing was harming our productivity. We had fallen into some kind of xeno’s paradox* where we would never actually get anything done, because we could always think of some new test that applied to a trivial subset of the project, and then work on writing code to satisfy that test.

*A dude shoots an arrow at a target. Before the arrow gets to the target, it has to cross half the distance to the target. Then it can cross the other half of the distance. But now it has to cross half of the remaining distance, so it does that.

Then it has to cross half of that remaining distance, and then half of the remaining distance after that, and so on for infinity.

Since the arrow has an infinite number of partial distances to cross, the arrow will never reach the target.

Read more about it here.

I was itching to solve a real problem, rather than just watch lights blink from red to green, so I cajoled my partner into writing a test for the blinker pattern, which is when a 3×1 rectangle of cells converts to a 1×3 rectangle of cells on the second turn, and then on the third turn, converts back to a 3×1 rectangle.

So, we started talking about how to implement the rules. We decided we needed to figure out for every cell that was near a living cell, how many living neighbors it had. So we wrote a method to generate the coordinates for the eight neighboring cell to a particular cell, and wrote a test for that.

Then we were going to make a neighbor_count hashmap attribute on our grid and we were going to use that to link cells to how many neighbors each had, and then the time ran out.

At this point, I had a good feeling about the algorithms involved in solving this project.

Third pairing

Right before the third pairing, a much older fellow raised his hand and asked if anyone wanted to work together on a solution that only tracked the living cells. That’s the approach I was using, so I paired with this guy. He said he didn’t care what language we used, but he was a lousy typist. So I said I could do the typing and we could use python.

At first we excitedly talked over each other and drew pictures until we confirmed we had the same solution in mind. It turned out my partner was an old common lisp hacker, and once he realized that I understood what he meant when he talked about stuff like &rest and cadr, we got along really well.

The first bit of code I wrote was a cell class with an x and a y attribute, and a method to generate a list of eight nearby cells.

I wrote a quick test in the same file as my code for that to make sure the execution was correct.

Of course, that test failed. I had lots of syntax errors because I was writing so fast and defending against good-natured jabs about how vim was so vastly inferior to emacs.

After a few cycles of fixing typos and rerunning the tests, we got the syntax errors out of the code. Then we attacked the project of generating the next state of the grid.

I had already seen how easy it was to write a test for the blinker pattern, so I wrote a quick test for that. The test made a grid with three cells in a vertical rectangle, then told the grid to generate the next state, then it tested that in the next state, the three cells were in a horizontal rectangle.

We wrote a grid class with a dictionary attribute of living cells in the current generation and a dictionary attribute of cells that would live in the next generation.

Then we wrote the function in our grid class to generate another grid. The function did an outer loop on all the living cells, then for each living cell, it looped through all the neighbors of that living cell, and then did an inner loop of all neighbors of that neighbor, and then counted up how many were alive.

Then we implemented the four rules of the game with two if-clauses.

We ran the test again, and of course, the code was again littered with indentation errors and mismatched parentheses because of how fast I had been typing and moving stuff around.

Then the timer went off. I stayed put while everybody was gathering in the middle to talk about how everything went. Within about 30 seconds I got the last few silly typing glitches fixed, and BAM. The test passed.

I walked over to my partner and told him we solved it.

Then we listened to other teams talk. The conversation centered around naming conventions that people were coming up with, like “sustainable neighborhood” and “four horsemen”.

I raised my hand and asked if anybody had written tests for any of the patterns in game of life beyond the blinker pattern, like tests for the glider pattern, or any of the other patterns shown on the wikipedia page.

Nobody replied to that. Instead the conversation shifted to a discussion of whether or not booleans hidden behind getters and setters were a sign of a bad design.

I think it was while somebody was talking about writing tests for their (nonexistent) display code that my partner leaned over and said “This is a drunkard’s search.” Of course, I didn’t know what meant, so he explained it. Here’s the wikipedia entry:

Conducting a drunkard’s search is to look in the place that’s easiest, rather than in the place most likely to yield results. Taken from an old joke about a drunkard who loses his car keys while unlocking his car and is found looking under a streetlamp down the road because the light is better, it has been an object of consideration in the social sciences since at least 1964.

Fourth pairing

I asked if anybody wanted to see a python solution, and four of us worked together, with me doing the typing.

First I described how we would need to find the eight neighboring cells of a particular cell. So I wrote a test for that, and then wrote the code to satisfy that test.

Then once that was finished, I described what the blinker looked like, and I wrote a test for that.

Then I reused the approach that we came up with in the third pairing, and then got it working fairly quickly.

At one point I showed the code we had written to one of the people running the event, and he pointed out two things (this is roughly paraphrased, and I hope I am getting these ideas correct):

  1. I had four if-clauses in a single function, and each if-clause tested two independent variables. So that means there were dozens of paths through the function that would have to be tested.
  2. My blinker test could be satisfied by code that just hardcoded the expected results, rather than built an actual game-of-life system. My test didn’t force a complete solution.

Both points illustrate the biggest difference in the TDD mindset versus whatever it is called that I do. (design by intuition?)

The fact that I didn’t have a test for every path that I created didn’t really concern me, because I was focused on getting the blinker pattern to work. If that blinker pattern test failed, then I might go in to my code and make sure that what I wrote was really what I meant, or maybe I’d even throw it all out and start from scratch. But I wouldn’t worry about covering all corners of this version until I was confident I was on the right track.

As for the second point, I use tests to catch errors, not to tell me what to write. I wouldn’t write code that returns a hard-coded list of values just to pass a test, unless I actually thought I could solve the real problem by doing that.

Anyhow, we got everything working pretty quickly this second time. You can see the output from my fourth pairing here.

After you download that code, you can run the tests like this:

$ python life.py
..
--------------------------------------------------------------------
Ran 2 tests in 0.001s

OK

Those two dots mean that my two tests passed. I spent the remainder of the time showing how to use the interactive interpreter and how to write doctests. I’ve tested a few of the patterns from the wikipedia page, and my code seems to do the right thing, but I’m not absolutely convinced that this implementation is correct.

Fifth pairing

I worked with two guys and we used ruby and rspec. I described the algorithm that I had used in the last two times, and we decided to work on building that.

We went with the approach of not writing any more code than was required to satisfy the tests.

So, first, we wrote some tests to instantiate a cell class, then we wrote some tests to call a neighbors method on the cell class and verify that it return a list of eight things, and then we verified that the first and last and elements in the neighbors list were at the position that we expected them to be at.

Then we started work on the grid class. We wanted to make sure that two different objects with the same values for their x and y attributes would be considered equal. But none of us knew how to redefine the == operator in ruby, and while we were researching this, the time ran out.

Again, I felt like we had fallen into the trap of slicing off trivial subsets of the real problem, and solving them, rather than attacking the real problem.

Commentary

Writing tests to check for errors (which is what I do) is not test-driven development. I daydream about solutions until I find one that I like, and then I build it, and I see if it works by writing tests to cover all the use cases I can think of.

My design comes from idle thoughts and doodles on my notepad, not from the testing.

Final note: I’ve tried my best to keep any generalizations and extrapolations out of this post. I don’t mean for this to be seen as an attack on anyone’s style of work. I’m very, very grateful for everything I’ve learned about how to write tests for software from the TDD community.

how to restart a gunicorn server without leaving vim

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I’ve been using the gunicorn WSGI server lately while I work on my next project. gunicorn is fantastic, except for one tiny nuisance. I have to restart gunicorn as I change my app code. At the beginning, this meant I would switch over to the terminal where gunicorn was running. Then I’d kill the parent process by hitting CTRL+C, and then start it up again, by typing:

gunicorn crazyproject.webapp:make_application

Other frameworks often have a development mode that forks off a helper process that watches the source code folder. When some file changes, the helper tells the server to reload.

I’m not using any frameworks this time, so I don’t have that feature. I never really liked the fact that every time I saved a file, I would restart the server during development. Instead, in this case, I want to easily restart gunicorn, but only when I want to, and I don’t want to leave my editor.

It turned out to be pretty easy to do.

First I read in the excellent gunicorn docs how to tell gunicorn to reload my app:

How do I reload my application in Gunicorn?

You can gracefully reload by sending HUP signal to gunicorn:

$ kill -HUP masterpid

Next I added a –pid /tmp/gunicorn.pid option to the command that I use to start gunicorn, so that gunicorn would write the parent’s process ID into /tmp/gunicorn.pid.

Now any time I want gunicorn to reload, I can do this little command in a terminal window:

$ kill -HUP `cat /tmp/gunicorn.pid`

Those backticks around cat /tmp/gunicorn.pid tell the shell to do that part of the command first, and then feed the result into the rest of the command.

You can always use ! in vim to run some command-line program. If I had to explain the difference between vim and emacs, the one difference that is most interesting to me is that vim makes it super-easy to send buffer contents to other programs or read buffer contents from other programs, while the people behind emacs seem to think that any external dependency should ultimately be moved into emacs itself. I get the feeling that vim wants to be my text editor, but emacs wants to be my OS.

Anyhow, while I’m in vim, I run that command to restart like this:

: !kill -HUP `cat /tmp/gunicorn.pid`

After using that code for a while, and feeling confident it worked right, I mapped F12 in vim to do that action for me by adding this little thing to the end of my ~/.vimrc:

:map :!kill -HUP `cat /tmp/gunicorn.pid`

Now that means I hit F12 when I want to reload gunicorn.

Some notes from when I start using git

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When I switched to git from subversion at my old business, I stored notes on how to do certain tasks. I’m pasting it below. Maybe some of this will help you out.

If you know a better way to do these tricks, please let me now.

My git diary
============

.. contents::

Slowly learning how to use git.

Typical upgrade flow
--------------------

I just committed a bunch of code and I want to see what the diffs were,
so I ran this::

$ git diff HEAD^

My production server runs branch 3.5.1 of my software. I want to start
work on a scary new feature that may take a long time, so I made a new
branch called 3.5.2 in my local sandbox::

$ git checkout -b 3.5.2

Now I can commit all my intermediate stuff in here.

Somebody found a bug in the production site (running 3.5.1) so I switch
to my 3.5.1 checkout::

$ git checkout 3.5.1
$ vi # fixing the problem
$ git commit -a -m "Fixed the prod bug"
$ git push origin 3.5.1

That last line sends my local commits to my remote bare repository.
That remote bare repository is on a box with an SSH server and RAID
storage.

Then I connect to the production box and pull down the most recent
changes::

$ ssh prod
matt@prod$ cd where-the-repo-is
matt@prod$ git pull origin 3.5.1
matt@prod$ restart-everything

That restart-everything command is a homemade script that does just what
you think it does.

Now back in my dev sandbox, I want to pull the bug fix from 3.5.1 into
my 3.5.2 branch. So I do it like this::

$ git checkout 3.5.2
$ git pull . 3.5.1

And now my 3.5.2 branch has that code in it. Hurray! Understand that
the dot (.) in git pull . 3.5.1 means that git should retrieve code from
this repository, not the fancypants remote one.

Pulling stuff
-------------

When I run::

$ git pull origin 3.5.1

That means to pull from the origin's 3.5.1 branch into whatever branch I
currently have checked out.

A typical day
-------------

I have two branches, an experimental branch and a public branch.
The production server used by customer runs the public branch.

Usually I work in my development branch. Sometimes I have to do some
code into production so this is how I do it::

$ git checkout stable # switch my local copy to the stable branch.
$ git pull origin stable # update local copy, just in case.
$ vi blah.py # do the bug fixes.
$ git commit -a -m "Notes about bug fixes"
$ git push origin # This is my deploy system.
$ git checkout dev # Go back to my development branch.
$ git pull origin stable # merge in that bug fix.

So far, this works well. I did something similar with SVN, and it also
worked fine. But git is way better at safely merging and it is much
faster.

Undo changes to a single file
-----------------------------

I typically edit a dozen files and then figure out that I want to undo
some stuff. If I did::

$ git reset --hard

Then my whole working copy would be destroyed. Usually, I just want to
do something like revert one file. So this is how::

$ git checkout that/particular/file

That deletes my working-copy changes just there. Everything else is
left as-is.

How to submit patches by email
------------------------------

I cloned the ditz project and tweaked the code, and I wanted to submit a
patch, so this is what they told me to do::

For this type of thing, it's "very simple". git commit -a, add a
one-line description followed by a blank line and more commentary, and
then git format-patch HEAD^.

When I ran git format-patch HEAD^, that produced a file on my local
machine that had a pretty formatted patch. Then I emailed that patch to
the list with some text.

How to branch from a remote repository
--------------------------------------

This is what somebody in the #git room told me to do, since I use a
remote bare repository::

$ git fetch origin
$ git checkout -b newbranch origin/original

Here's another person's opinion::

$ git fetch && git checkout --track -b mynewbranchagain remotename/mynewbranch

Set the remote branch
---------------------

Normally I have to pull from my remote repo and specify the branch I
want to pull in like this::

$ git checkout experimental
$ git pull origin experimental

It is possible to associate my local branch of experimental with that
remote branch of experimental like this::

$ git config --add branch.experimental.remote origin
$ git config --add branch.experimental.merge experimental

And now I can run::

$ git pull origin

without specifying the remote branch. In fact this works too::

$ git pull

Compare one file across two local branches
------------------------------------------

I want to look at a diff of x.py in my public branch vs my experimental
branch, so this is what I did::

$ git diff public experimental -- x.py

I can see everything different between the two branches like this::

$ git diff public experimental

Break up a whole bunch of changes into different commits
--------------------------------------------------------

I'm irresponsible about committing after each conceptual unit of work.
Lots of time, I'll edit a file to fix one bug, then while I'm in there,
I'll edit some other code because I see a better way to do something
else. Then I'll maybe add a few doctests to a completely different
section just because I want to.

After a few hours, typically inside of the same file, I have edits
related to multiple separate tasks.

Before I commit my changes, I run::

$ git add -p frob.py

Which walks through all the changes in that file and asks me if I want
to stage each one. In the first pass, I stage all the hunks related to
the first issue. Then I commit those changes. Then I rerun git add -p
frob.py again and march through the file for the next the second issue.

Keep in mind that I committed my changes after the first pass, so when I
go through the file the second time, I won't get prompted for those
changes.

This is one of those git features that you just couldn't do with svn.

Find the commits in branch A that are not in branch B
-----------------------------------------------------

Sometimes I'll patch a production bug in my production branch and then I
will forget to merge it into the development branch. This is how I can
check for that::

$ git checkout production_branch
$ git cherry dev_branch

This will spit out a list of commits that are in production_branch but
not in dev_branch.

It will not return any commits made to dev_branch but not in
production_branch.

See a file as of a point in time
--------------------------------

Looking at a commit shows the changes. Sometimes I want to see the file
itself.

Here's how to look at foo.py as of two commits ago::

$ git show HEAD^^:b/foo.py

Here's how to see what foo.py looked as of a particular commit::

$ git show bf51ebdbc:b/foo.py

b/foo.py is the path to the foo.py from the top of the repository. I'm
not certain, but I don't think the current working directory matters.

Copy a file from one branch to another
--------------------------------------

I committed a file into one branch then checked out a new branch. This
is how I copied that file into the new branch WITHOUT merging it in::

$ git checkout newbranch # 1
$ git checkout otherbranch foo.py # 2

Step 1 moves me into the newbranch. Step 2 gets me a copy of the file
foo.py from otherbranch and saves it into this branch named newbranch.

See a file in a different branch
--------------------------------

After I checkout the maxhenry branch I want to see the version of
printable.kid in the mayfield branch::

$ git checkout maxhenry
$ git show mayfield:bazman/bazman/templates/printable/printable.kid

Set a file to an old version of itself
--------------------------------------

Sometimes I want to get the version of a file as of a certain commit and
check that in. There are lots of ways to do this, including using git
revert or git reset, but I've had good luck with this approach::

$ git log # Use this to find the commit you want.

$ git checkout ac778cbb5517e1aeef446c9a8a1092eef81717fa:repo-top/a/foo.py

After you run this, the index will have this old copy queued up to be
commited. You can use git diff --cached to see the changes.

Create a new branch on the remote repo
--------------------------------------

We just pushed the branch **mollusk** up to production, so now it is
time to create a new branch named **nosehair**::

$ git branch nosehair # creates the new branch
$ git checkout nosehair # switches to the new branch
$ git push origin nosehair # pushes it up to origin

Switch to a new branch that already exists on a remote repo
-----------------------------------------------------------

After somebody else already created the branch nosehair, and pushed it
up to the remote repository, here's how to switch to work on the
nosehair branch::

$ git fetch origin
$ git branch -a # make sure origin/nosehair exists!
$ git checkout -b nosehair origin/nosehair

Search through commit messages
------------------------------

This is how I found all commits that had a commit message that included
the word CCPL::

$ git log --grep=CCPL

This is how I limited it to just my (Matt's) commits for CCPL work::

$ git log --grep=CCPL --author=matt --all-match

Without the --all-match option, you'll see all commits by matt or that
have CCPL in the commit message.

Looking for a few CLE pythoners for a quick project

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I can build it myself, but it’s going to take a lot longer. I’m looking for a few people to help me build a geographical search app.

If you’re smart, live near me, and have at least eight hours a week to work, let me know.

This will be for some combination of money up front and equity.

I expect to launch in anywhere from six weeks to three months after the start.

I have no patience for ideologues, jackanapes, or freeloaders.

The first meal I cooked with my new cast-iron skillet

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My lodge cast-iron skillet arrived this week and this morning I tried it out for the first time.

First I went outside and pulled up two of my shogoin turnips.

I broke the greens off the tops and threw the roots in my wheelbarrow. The roots were obviously full of of root maggots; I could see the little holes where they tunnel inside all over the outside.

Now the root maggots don’t actually ruin the root for eating. The maggot is a tiny little grub about the size of a big grain of salt. The tunnels mostly just look gross when you slice up the root into chunks.

Plenty of turnip recipes involve mashing up the root after boiling it down; maybe the mashing is really just a way of hiding the evindence of the root maggots.

The greens at the top of these plants looked great. That awfully bitter pepper taste that causes most people to gag when they eat turnip greens raw is also a fantastic deterrent for aphids and leaf-eating caterpillars. These leaves showed nearly no signs of damage.

I went inside and I put a tiny bit of canola oil (like about one fourth of a teaspoon) into my new skillet and swirled it around. I added four strips of bacon and turned the heat to medium.

The plants were generally clean, but when I pulled the roots, I accidentally got some soil onto the leaves. So I rinsed the turnip greens. Then I removed the stems, rolled up the leaves, and chopped the rolled-up leaves.

Then I added about four cloves of garlic (whole, not crushed or minced) to the skillet with the bacon. I also chopped up half of an onion and threw that in there.

Once I saw the bacon was at that chewy texture that I’m fond of, and the onions were softening up, I added the chopped-up turnip greens and put the lid on.

I looked all over the kitchen for a can of chicken stock, but I couldn’t find any, so I added about a half-cup of water instead.

Then I set the oven timer for 12 minutes, drank coffee, and read my newest issue of Countryside Magazine. This one has a fantastic article in there by Harvey Ussery all about the science of growing cover crops to improve soil structure. Here’s a good excerpt:

Let’s focus again on this fact: The greatest diversity and concentration of soil species is in the area immediately surrounding plant roots, the rhizosphere. That is, the more roots in the soil, the more alive is the soil; and as we have seen, a soil that is more alive is more fertile. This maybe be counterintuitive, since we’ve probably been conditioned to think that crop plants take nutrients out of the soil (with the sly implication that we have to purchase nutrients — “fertilizers” — to replenish them).
In other words, soil that is crammed full of weed roots is actually more fertile than soil that is bare on the surface.

As long as the plant material is left to decay in place, then over time, soil fertility improves. Before you start talking about thermodynamics, remember that this is not a closed system. The sun sends energy to the earth, and plants harness that energy and then store it chemically.

Here’s a tangent — I have a bunch of half-baked ideas about what software writers can learn from organic gardening. For example, we focus too much on enforcing uniformity. Instead, we should learn how to cooperate in larger systems where other actors behave nothing like us.

My bean plants have figured out how to cooperate with bacteria. The bean plants host the bacteria in little nodules in their roots and they supply sugars to the bacteria. The bacteria then consume that sugar and output nitrogen molecules in a form that the plant can use.

Meanwhile, we throw tantrums and won’t accept help from somebody else once we learn that their code indents with tabs instead of spaces.

But that stuff goes in a different text file.

Anyhow, the kitchen timer never went off. Instead, I decided the greens were ready at around the 9-minute mark, after I stirred the stuff in the skillet and then tasted it.

Next I used a wooden spoon to scrape all the bacon, onions, garlic cloves, and cooked turnip greens into a big pasta bowl.

It is important to add a little salt and plenty of hot sauce at this point. Use a hot sauce with a lot of vinegar, like tabasco sauce. The acidity in the vinegar and the salt has some extra effect on the greens that cause the last traces of violent bitterness to change into a smooth smokey flavor instead.

The meal was delicious.

A new pitz release (1.1.2)

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I’m using semantic versioning now, so I bumped from 1.0.7 to 1.1.0 after adding a few tweaks to the command-line interface. Then I discovered a silly mistake in the setup.py file, and released 1.1.1. Then I realized I did the fix wrong, and then released 1.1.2 a few minutes later.

The –quick option

Normally, running pitz-add-task will prompt for a title and then open $EDITOR so I can write a description. After that, pitz will ask for choices for milestone, owner, status, estimate, and tags.

Sometimes I want to make a quick task without getting prompted for all this stuff.

I already had a --no-description option that would tell pitz-add-task to not open $EDITOR for a description. And I already had a --use-defaults option to just choose the default values for milestone, owner, status, estimate, and tags.

But when I just want to make a quick to-do task as a placeholder, writing out all this stuff:$ pitz-add-task --no-description --use-defaults -t "Fix fibityfoo"

is kind of a drag. So I made a --quick option (also available as -q) that does the same thing as --no-description --use-defaults.

The -1 alias for –one-line-view

This is the typical way that a to-do list looks:$ pitz-my-todo -n 3
==============================
slice from To-do list for matt
==============================

(3 task entities, ordered by ['milestone', 'status', 'pscore'])

Write new CLI scripts (witz!) to talk to pitz-webapp 9f1c76
matt | paused | difficult | 1.0 | 1
webapp, CLI
Starting up and loading all the pitz data at the beginning of ever...

Experiment with different task summarized views 0f6fee
matt | unstarted | straightforward | 1.0 | 1
CLI
Right now, the summarized view of a task looks a little like this:...

Add more supported URLs to pitz-webapp 295b5f
matt | unstarted | straightforward | 1.0 | 0
webapp
I want to allow these actions through the webapp: * Insert a ne...

Incidentally, notice the -n 3 option limits the output to the first three tasks.

Tasks also have a one-line view:$ pitz-my-todo -n 3 --one-line-view
==============================
slice from To-do list for matt
==============================

(3 task entities, ordered by ['milestone', 'status', 'pscore'])

Write new CLI scripts (witz!) to talk to pitz-webapp 9f1c76
Experiment with different task summarized views 0f6fee
Add more supported URLs to pitz-webapp 295b5f

Typing out --one-line-view is tedious, so now, -1 is an alias that works as well:$ pitz-my-todo -n 3 -1
==============================
slice from To-do list for matt
==============================

(3 task entities, ordered by ['milestone', 'status', 'pscore'])

Write new CLI scripts (witz!) to talk to pitz-webapp 9f1c76
Experiment with different task summarized views 0f6fee
Add more supported URLs to pitz-webapp 295b5f

Build your own kind of dictionary

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This is the video from my PyOhio talk on building objects that can act like dictionaries.

The text and programs from my talk on building your own are available here on github. You can probably absorb the information most quickly by reading the talk.rst file.

Please let me know if you find spelling errors or goofy sentences that are hard to understand that I should rewrite.

This is the description for the talk:

My talk is based on a project that seemed very simple at first. I wanted an object like the regular python dictionary, but with a few small tweaks:

  • values for some keys should be restricted to elements of a set
  • values for some keys should be restricted to instances of a type

For example, pretend I want a dictionary called favorites, and I want the value for the “color” key to be any instance of my Color class. Meanwhile, for the “movie” key, I want to make sure that the value belongs to my set of movies.

In the talk, I’ll walk through how I used tests to validate my different implementations until I came up with a winner.

Unlike my talk last year on metaclass tomfoolery, and the year before that on fun with decorators (and decorator factories) I’m hoping to make this talk straightforward and friendly to beginning programmers.

You’ll see:

  • how I use tests to solve a real-world problem
  • a few little gotchas with the super keyword
  • a little about how python works under the hood

Raphael.js event handlers sometimes require closures

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I’m playing around with raphael. In the code below, I use a few loops to make a grid of rectangles. I want each rectangle turn from white to gray when clicked. This is a little tricky in raphael, because you can’t use this or evt.target to get a reference to what got clicked on.
var main = function () {
var paper = Raphael("grid", 320, 200);
for (var rownum=0; rownum<3; rownum+=1) { for (var colnum=0; colnum<3; colnum+=1) { var r = paper.rect(10+colnum*50, 10+rownum*50, 50, 50); r.attr({stroke:"gray", fill:"white"}); r.node.onclick = function () { var this_rect = r; return function () { this_rect.attr({fill:"gray"}); } }(); } } }; window.onload = main;

Remember that your typical boring onclick assignments usually look like this:
r.node.onclick = function () {
alert("your mom");
};

I don't call the function. I just define it.

Study the r.node.onclick assignment in the main code again, and make sure to notice that the r.node.onclick attribute is assigned to the result of the function defined.

That's the first big difference. Now you have to figure what the heck is returned by this function. The answer is. . . another function. That other function is what gets linked up to be fired when a click event happens.

Closures are tricky at first, but they're really useful for situations like this, when you need to pass along references with the functions to operate on them.

Building A Sane Development Environment

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For all these tasks, make them easy to do or you won’t really do it.

Start everything in a clean environment

Don’t hack in an environment filled up with artifacts from the previous release. Clear them all out. Make sure that your environment looks like what you released for 1.0 before you start 1.1.

Encourage lots of sandboxes

Be able to explore mutually exclusive solutions to the same problem and not worry about conflicts.

Make your environment realistic

Design your sandbox so that it resembles your production environment.

Just to be clear, I don’t mean that development must be identical to production. I mean that if you anticipate bottlenecks in production, figure out how to model them.

Deploy during development

Deployment should be boring. But it usually isn’t, because developers overlook trivial dependencies they created along the way.

You’ll quickly discover what you forgot to add to your deploy scripts last time if you start every session like this:

  1. Reset your sandbox.
  2. Check out your code.
  3. Run the deployment script.
  4. Now start working.

By the time you are ready to release, you will have simulated the deployment process many many times.