A quick example of transforming Python with libcst
I had occasion to encounter a Python library that used assert with a side effect:
assert initialize_hardware(), "hardware failed to initialize"looking a bit more widely, this idiom was apparently used hundreds of times across a family of Python libraries.
"Aha", I said, "I bet I can fix this with an automated tool". In this round of investigation, I found LibCST and set about creating a program that would do what was needed, namely, to turn at assert into if not initialize_hardware(): raise RuntimeError("hardware failed to initialize").
While LibCST has an explicit facility for "codemodding", I didn't notice it at first and wrote in terms of transformers, with my own command-line driver program.
Unfortunately, while my transformer succeeded, attempting to format the CST back into code would result in an error without very many matches on my favorite search engine: Unexpected keyword argument 'default_semicolon'. That linked issue didn't provide an answer, but my further investigation did.
In the Python grammer as represented by LibCST, an assert statement is part of a SimpleStatementLine, while an if statement is not wrapped in a SimpleStatementLine. So if the transformation of an Assert node into an If node is done alone, the new If node lies inside a SimpleStatementLine node, and that is not valid. The problem is not detected until rendering the CST back into code. (It may be possible that using type checking would have found a problem, as this is essentially a type error)
The solution that I arrived at was to also transform any SimpleStatementLine which ended up containing an If node, by using the FlattenSentinel to do it. I think it might have been even more correct to directly perform the transformation within SimpleStatementLine, but what I ended up works now.
Local coordinate systems in OpenSCAD
Here's a small snippet for setting a local coordinate system. You need to know the location to treat as origin as well as the direction vectors to treat as X and Y.
// Take a position vector (p) and 3 direction vectors (uvw)
// and create a transformation matrix. The origin is transformed to p,
// and xyz point along uvw.
// Normally, the caller will ensure that uvw are orthogonal unit vectors
function puvw(p, u, v, w) = [
[u[0], v[0], w[0], p[0]],
[u[1], v[1], w[1], p[1]],
[u[2], v[2], w[2], p[2]]];
// Take a position vector (p) and 2 direction vectors (uv) which should be
// orthogonal but need not be unit vectors. Calculate the unit vectors as well
// as the third vector and return the resulting matrix
function puv(p, u, v) =
let(nu = u / norm(u), nv = v / norm(v), nw = cross(nu, nv))
puvw(p, nu, nv, nw);
// Operate in a local coordinate system where the origin is the point p,
// x points along u, y points along v, and z points along the normal vector
// to uv. x and y should be orthogonal but need not be unit vectors.
module puv(p, u, v) {
multmatrix(puv(p, u, v)) children();
}
For instance, suppose you want to lay out some feature relative to a cone 100mm in diameter and 500mm tall. It's convenient to set the origin to the intersection of the cone base with the +x axis, +x be the direction from the base of the cone to the tip, +y be the direction tangential to the cone, and +z be the direction 'out' from the cone. You might invoke puv like so (corr is a factor to make the flats of the faceted cone exactly touch the 100mm diameter circle):
effen = 16; // 16, 32, 64, ... corr = 1 / cos(180/effen); for(i=[0:45:360]) rotate(i) puv([100,0,0], [-100, 0, 500], [0, -1, 0]) linear_extrude(height=1) square([25, 4], center=true); %rotate(45/4) cylinder(d1=200*corr, d2=0, h=500, $fn=effen);
Recent keyboard deeds
I made several USB HID keyboard conversions recently. They all use CircuitPython. The hardware setup is not documented as none are worthy of being called finished projects at this point, but the source code gives an idea what connections are needed. One or more of these may be the subject of a future Adafruit Learning System Guide.
Click a triangle to see the full code as an embedded github gist. (Note: if you're viewing this in a RSS reader, you may have to click through to get the embeds. Sorry!)
Commodore 16 Keyboard
Used an Adafruit KB2040. Gratuitous use of asyncio. The keymap needs work to be usable, but it's a good start. Direct gist link.IBM XT "Model F" Keyboard
Used an Adafruit QT PY RP2040. This layout is AWFUL, the "beloved" iteration of the Model F was for AT computers, with a layout a lot more like a modern keyboard (aside from the placement of the Esc and Ctrl keys anyway) Direct gist link.Tandy 1000 Keyboard
Don't wreck your system with miniconda/anaconda
I guess this software is a tolerable way to install those libraries and packages needed for so many machine learning things written in Python. But annoyingly, it wants to "go to the head of the line" in front of system Python. This is reallllyyyy not what I want.
I noticed that the little blob it deposits in ~/.bashrc can easily be surrounded with a function definition. So, now to activate anaconda in the current shell, but never replace/hide system python in a normal shell, I can just type "fml".
fml () {
# >>> conda initialize >>>
# !! Contents within this block are managed by 'conda init' !!
__conda_setup="$('/home/jepler/miniconda3/bin/conda' 'shell.bash' 'hook' 2> /dev/null)"
if [ $? -eq 0 ]; then
eval "$__conda_setup"
else
if [ -f "/home/jepler/miniconda3/etc/profile.d/conda.sh" ]; then
. "/home/jepler/miniconda3/etc/profile.d/conda.sh"
else
export PATH="/home/jepler/miniconda3/bin:$PATH"
fi
fi
unset __conda_setup
# <<< conda initialize <<<
}
Now I don't feel quite so worried that having it present on the system is going to interfere with system software or with software I've installed to work with system software via pip.
Generate the 64 GCR values used by Apple DOS 3.3 and ProDos
for i in range(128):
b = f"{i:07b}" # All these tests apply to the low 7 bits
if '000' in b: continue # 3 consecutive zeros disallowed
if b.count('00') > 1: continue # only one pair of consecutive 0s allowed
if not '11' in b: continue # one pair of consecutive 1s required
print(hex(i | 128), bin(i | 128)) # top bit is always a 1
An interesting finding about Apple DOS 3.3 diskettes
I can't be the first to have noticed this, but if somebody wrote about it years ago there's no way a search engine today will turn it up since they over-value recency and pay little attention to little sites with niche information. So here's my write-up. It feels a little inconclusive, but so be it. I imagine that these disks were mastered in an unsual way, rather than by duplicating a disk written on an Apple II using normal Apple II RWTS code.
I've been working on an open source tool to convert .a2r to .woz. While doing so, I got pretty low level with the Apple flux encoding.
This encoding varied over the years, and of course what really matters is what would work on real machines in the wild.
But one central claim about Apple floppy formats is that early DOS before 3.3 used the repeated bit sequence "1111 1111 0" to allow the floppy interace's state machine to synchronize with the stream of bits on the floppy. Starting with DOS 3.3 and continuing with ProDOS, and ProDOS, the bit sequence "1111 1111 00" is used instead. The newer sequence (also called FF40, because its hex value is FF and it takes 10 bits or 40 microseconds to transmit; the old code is also called FF36) is longer, but fewer repetitions are required to guarantee synchronization.
So I was surprised to see the following when I peered into "DOS 3.3 System Master [1983] - Disk 1, Side A.a2r" from CowgodA2R on archive.org (as are all the a2r files I inspected for this blog post):
111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 111111110 FF36 11111111 FF 11010101 D5 10101010 AA 10010110 96 11111111 FF 11111110 FE 10101010 AA 10101010 AA 10101111 AF 10101010 AA 11111010 FA 11111110 FE 11011110 DE 10101010 AA
That's right, the FF36 sequence appears in this DOS 3.3 floppy from 1983. Essentially the same sequence is seen on ProDOS User's Disk - Disk 1, Side A.a2r.
An even odder sequence is seen on the 1980 edition of DOS 3.3:
1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 111111110 FF36 1111111100 FF40 11111111 FF 11111111 FF 11001111 CF 11110011 F3 11111100 FC 11111111 FF 11010101 D5 10101010 AA 10010110 96 11111111 FF 11111110 FE 10101010 AA 10101010 AA 10101011 AB 10101110 AE 11111110 FE 11111010 FA 11011110 DE 10101010 AA
The CF/F3/FC/FF sequence would be an FF40 sequence if the earlier FF bytes hadn't already left you synchronized, but .. there's absolutely no reason for it!
Finally, a disk from the "non-originals" section, which I assume means it's cracked software, has the sequence I expect (more or less) based on reading documentation from the time as well as modern emulator source code:
1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 1111111100 FF40 11111111 FF 11010101 D5 10101010 AA 10010110 96 11111111 FF 11111110 FE 10101010 AA 10101010 AA 10101010 AA 10101011 AB 11111111 FF 11111111 FF 11111111 FF 11111111 FF 11101000 E8 10111111 BF 11111100 FC
An interesting Disk ][ Interface Card Fault
tl;dr: I recently got into 8-bit Apple retrocomputing due to my work with Adafruit. I had a Disk II setup that couldn't write to any floppy. I fixed it by replacing a 74LS05 IC on the Disk II Interface Card.
Stuff I did in 2021...
Here are some of the things that came up in my inventory of last year's deeds:
- 25 posts on this blog
- 21 posts on the Adafruit blog
- 11 guides on the Adafruit learn system
- 2301 contributions on github
- 6 3D printed designs shared with the world
- 3 circuit sculptures
- 1 PCB design (& got much more comfortable with kicad)
- Got comfortable using FreeCAD
- Fave Projects: CircuitPython WWVB Clock & WWVB Observatory
- 6+ inter-state trips
Where should CircuitPython go in 2022?
The Most Surprising Optimization I've Seen Lately
80columns
Estimating WWVB Signal Health
Use printf() in Arduino programs
CWWVB: Putting what I've learned about WWVB to use in a new decoder
WWVB Observatory
My experience adding type annotations to a 2.5k-line Python library
All older entries
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