Tuesday, August 13, 2019

Coping with Windows via AWS

For a training class, I needed to address The Windows Problem™. TWP is the my summary of all the non-standard features of Windows in its various inconsistent incarnations.

Any training class that involves "install Python" inevitably involves at least one Windows user who can't get their PATH set correctly. It's an eternal mystery to me, since the installers all seem to take care of this, but, some people are able to click the wrong thing somewhere in a simple installation.

The uninstall and start again sometimes helps. Having a Windows expert in the room sometimes helps.

(The hapless flailing I sometimes observe is my personal problem to deal with. I should not let myself get short-tempered with people who try things exactly once and then stop, unable to discern a single branch in the path they chose. It's as if the sequence of dialog boxes with different choices never existed for them, and I need to respect the fact that they did not read the messages and did not think of themselves as actively making choices.)

I have to say that being able to get a Windows machine in free tier of AWS is a wonderful resource.

I can screen capture the installation on Windows. 

I can narrate the sequence of choices I made. I'm hoping this prevents TWP from side-tracking a person who's struggling with Windows.

I haven't used the movies yet. But it's so handy to be able to spin up a Windows machine in the cloud and run the Conda install. It's a whole lot nicer than buying a throw-away Windows machine to do screen shots on.

Friday, July 5, 2019

Mastering Object-Oriented Python 2nd ed

The book https://www.packtpub.com/programming/mastering-object-oriented-python-second-edition

Some new chapters. 

Type hints almost everywhere.

If you want to write a review, DM me on twitter @s_lott I can add you to the list for freebies in exchange for a review.

Thursday, June 20, 2019

HumbleBundle -- Functional Python Programming -- Through July 1

See this https://www.humblebundle.com

This is amazing to me. 
Humble Bundle sells games, ebooks, software, and other digital content. Our mission is to support charity while providing awesome content to customers at great prices. We launched in 2010 with a single two-week Humble Indie Bundle, but we have humbly grown into a store full of games and bundles, a subscription service, a game publisher, and more.
Currently, Packt is offering some of my books.

Want a *ton* of technical books and donate to charity?

Click Now. Thank me later.

Tuesday, June 18, 2019

The Pythonista app for iPad

Let me start my review with "wow!"

Python 3.6 on the iPad. Works. Nicely. Easy to use. Reliable. Rock-Solid.

I'm not switching to iPad as my primary platform any time in the near future.  But. For certain kinds of small and tightly focused hackery, this is really nice.

I use a bracket to hold the iPad up and an external keyboard. I can be used with the on-screen keyboard, but, that's slow-going for me.

Here's the thing that was exquisitely simple in Pythonista:

I'm able to draw a hex grid ("Flat Top", "Double Height") in a few dozen lines of code. This includes a bunch of geometry rules like adjacency and directional movement.

The Pythonista package includes a super-easy-to-use canvas module that's a tiny bit simpler than turtle graphics. It takes a bit of getting used to, but it has enough graphics primitives to make it easy to create hexagons and tile the surface.

Given a HexGrid instance, I can then create "cities" and their surrounding territories in an "empire". I've tried a few organic growth algorithms, and I like the look of these maps. They provide a lot of avenues for conflict for writing fiction or playing role-playing games.

Some of the algorithmic foundations: https://www.redblobgames.com/grids/hexagons/.

Fun Hackery

This is fun hackery because I can change the code, click the run icon, and watch the consequence of the changes. A traceback is highlighted in the original file. Easy. Fun.

It's pretty slow. No surprise there. It's running on an iPad.

It's pretty easy to work on. Whip out the iPad and start coding.

The super-easy, built-in canvas module means feedback is instant and gratifying.

I can see having an intro to programming class where the fee includes an extra $800 for the iPad you take home along with your new-found skills in basic coding. (This is still a *lot* of money, but it's less than a full laptop.)

Filling in the Holes

Looking at the output, you can see the growth algorithm left some unfilled holes. A later version examines all unfilled spaces to see if they're entirely surrounded by one color and fills them. This is a fun algorithm because it works in a simple way with the adjacency iterator and the set of locations covered by a city. Locations 12L and 17K are these "Simply Surrounded Single Holes."

However, there are still some "Edge" cases that are challenging.

Location 12D reflects a hole on a border. These are interesting, and could be the seed for epic wargaming, role-playing game, novel-writing drama. A simple algorithm can find these and assign a random owner... But... They really need a special "On Fire" color scheme to show the potential for drama.

There's a subtlety in the upper-left corner (5W and 6V) between Blue and Green. While these seem like simple border holes, each hole as only five of six required neighbors.

Compare these with 16P in the upper-right corner. This also has five of six neighbors. However, this space looks like it could be a bay leading up to a river and the river is a natural border between nations.

The head of the bay at 16P has 5 neighbors of two colors, similar to 5W and 6V. The difference can be detected by a recursive walk to see if a hole is connected to other holes and the composite is actually surrounded. There are lots of *edge* cases, but the (5W, 6V) pair seems to embody the next stage of surround detection.

This more nuanced algorithm design doesn't work out well in the Pythonista environment. This algorithm design requires careful unit tests, not the code-and-run cycle of hackery. For this kind of careful design, we'd need to leverage doctest (or unittest) for testing. While I'd like pytest, that's a lot to ask for. For these kinds of apps, doctest is more than adequate, and a simple import doctest; doctest.testmod() in a scrip can help be sure things work as expected.


If you're an iPad user, consider adding Pythonista. You can really write real Python. It's a useful environment. It's fun for teaching.

Tuesday, June 11, 2019

Circuit Python on the Gemma M0 -- The Red Ranger Beacon

PyCon 2018 Swag included a Gemma m0. (https://www.adafruit.com/product/3501)

PyCon 2019 Swag included a Circuit Playground Express. See https://learn.adafruit.com/adafruit-circuit-playground-express/circuitpython-quickstart.

Both of these are (to me) amazing. They mount as USB devices; there’s a code.py file that’s automatically run when the board restarts.

The Gemma has fairly few pins and does some real simple things.  The CPX has a bunch of pins and ton of hardware on the board. Buttons, Switches, LED’s, motion sensor, temperature, brightness... I’ve lost count.

Step 1 -- Get Organized

Create a proper project directory on your local machine. Yes, you can hack the code.py file immediately, but you should consider making a backup before you start making changes.

Few things are more frustrating than making a mistake and being unable to restore the original functionality as a check to be sure things are still working.

Also. At some point, you'll want to upgrade the OS on the chip. This will require you to have a bootable image. The process isn't complex, but it does require some care. See https://learn.adafruit.com/welcome-to-circuitpython/installing-circuitpython#download-the-latest-version-3-4 for downloading a new OS.

So. Step 1a. Create a local folder for your projects. Within that folder, create a folder for each project. Put the relevant code.py into the sub-folder. Like this

 ┣━━ baseline
 ┃   ┗━━ code.py
 ┣━━ my-first-project
 ┃   ┗━━ code.py
 ┣━━ another-project
 ┃   ┗━━ code.py
 ┗━━ os-upgrade
     ┗━━ other files...

See https://learn.adafruit.com/adafruit-gemma-m0/troubleshooting for additional help if you have a Windows PC.

Step 2 -- Start Small

Tweak a few things in the supplied code.py if you're new to IoT stuff.

A lot of folks like the Mu editor for this. https://codewith.mu.

I like using BBEdit. https://www.barebones.com/products/bbedit/.  To make this work I *also* need to have

  • a terminal window open so I can use the Mac OS screen application, and
  • a finder window open to copy the code.py from my PC to the Gemma M0.

This is a lot of busy screen real-estate with three separate apps open. It's not for everyone. I like it because there's little hand-holding. You may prefer Mu.

It's important to go through the edit/download/play cycle many times to be sure you're clear on what code's on your PC and what code's on your board.

It's even more important to see how you're forced to debug syntax errors using the screen app until you invent a suitable mock library for off-line unit testing.

Step 3 -- Plan Carefully

The version of Python is remarkably complete.


It's also a very small processor, with very few pins, so you can't do anything super elaborate.  You can, however, do quite a bit.

See Nina Zakharenko - Keynote - PyCon 2019 for some inspiration

Step 4 -- Check This Out


Many thanks to @nnja for showing us some elegant, inspirational ideas.

Tuesday, June 4, 2019

Probabilistic Data Structures

Interesting data structures with O(n) performance. This can help to unscramble O(n²) problems allowing progress.


Tuesday, May 28, 2019

Rules for Debugging

Here's the situation.

Someone wrote code. It didn't do what they assumed it would do.

They come to me for help.

Here are my rules for debugging. All of them.

1. Try something else.

I don't have any other or more clever advice. When I look at someone's broken code, I'm going to suggest the only thing I know. Try something else.

I can't magically make broken code work. Code's not like that. If it doesn't work, it's wrong, usually in a foundational way. Usually, the author made an assumption, followed through on that assumption, and was astonished it didn't work.

A consequence of this will be massive changes to the broken code. Foundational changes.

When you make an assumption, you make an "ass" out of "u" and "mption".

Debugging is a matter of finding and discarding assumptions. This can be hard. Some people think their assumptions are solid gold and write long angry blog posts about how a language or platform or library is "broken."

The rest of us try something different.

My personal technique is to cite evidence for everything I think I'm observing. Sometimes, I actually write it down -- on paper -- next to the computer. (Sometimes I use the Mac OS Notes app.) Which lines of code. Which library links. Sometimes, i'll include in the code as references to documentation pages.

Evidence is required to destroy assumptions. Destroying assumptions is the essence of debugging.

Sources of Assumptions

I'm often amazed at how many people don't read the "But on Windows..." parts of the Python documentation. Somehow, they're willing to assume -- without evidence -- that Windows is POSIX-compliant and behaves like Linux. When things don't follow their assumed behavior, and they're using Windows, it often seems like they've compounded a bunch of personal assumptions. I don't have too much patience at this point: the debugging is going to be hard.

I'm often amazed that someone can try to use multiprocessing.apply_async() without reading any of the example code. What I'm guessing is that assumptions trump research, making them solid gold, and not subject to questioning or locating evidence. In the case of multiprocessing, it's important to look at code which appears broken and compare it, line-by-line with example code that works.

Comparing broken code with relevant examples is -- in effect -- trying something else. The original didn't work. So... Go to something that does work and compare the two to identify the differences.