सतत

Readable code

शांतनु — Fri, 30 Jan 2026 09:22:20 GMT

Background

I am revisiting Clojure by cleaning up and handling bad-data. Data is in a CSV file. There are two aspects to the problem - return clean rows and log/find bad ones.

This reminded me of a Clojure project I worked on in 2020 that handled drop shipping of orders from a third-party website. We would receive orders in CSV files, create these orders on our store, and respond with order tracking details in CSV format. Our store API worked with JSON data, so I had to handle the data transformation from CSV to JSON and back.

Problem: Handle the transition of data from flat to nested form

I was learning Clojure while working on that project, and I wrote the following function to flatten nested order data:

(defn single-row-per-sku
  "Convert consolidated processed orders to rows containing each SKU"
  [orders]
  (reduce (fn [result order] (concat result (map #(merge % (dissoc order :items)) (:items order)))) [] orders))

It works—I wrote unit tests to make sure it did. But it is dense and unreadable. I can't even recall how I explained this section during code review.

I used Clojure for the Brave and True for learning the language. It was a fun and refreshing read on introducing core concepts. The function that I wrote doesn't do justice to the quality of the content.

Brave Clojure also has this relevant quote from Alan Perlis:

It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures.

I came from Python background. I also didn't know about threading macros in Clojure when I wrote above function. The quote really made sense to me once I learned about threading.

As I am revising Clojure concepts I am writing a lot of small function and testing them using the REPL. In the same vein I feel following is more readable equivalent:

(defn get-address [order]
  (dissoc order :items))

(defn get-items [order]
  (order :items))

(defn flatten-items [order]
  (let [address (get-address order)
        items (get-items order)]
    (->> items
         (map #(merge address %)))))

(defn single-row-per-sku [orders]
  (->> orders
       (map flatten-items)
       flatten))

Small functions. Threading macros. Names that make sense. Easy to read and functional. I don't think it's the final version-the ballad continues as I keep learning.

Getting started with powerful abstract tools: Emacs, Vim

शांतनु — Tue, 13 Jan 2026 15:35:00 GMT

Foundation: Text Editors

In his book The Dip, Seth Godin talks about snowboarding:

Snowboarding is a hip sport. It’s fast, exciting and reasonably priced; and it makes you look very cool. So why are there so few snowboarders? Because learning the basic skills constitutes a painful Dip. It takes a few days to get the hang of it, and, during those few days, you’ll get pretty banged up. It’s easier to quit than it is to keep going.

The brave thing to do is to tough it out and end up on the other side–getting all the benefits that come from scarcity. The mature thing to do is not even to bother starting to snowboard because you’re probably not going to make it through the Dip. And the stupid thing to do is to start, give it your best shot, waste a lot of time and money, and quit right in the middle of the Dip.

In the programming world, editors are an important basic skill-they are like the snowboard in this analogy. I would often read about vim and emacs. In college, I tried them a couple of times and got stuck. vim's swap file prompt was scary. When git opened vim's side-by-side buffer to resolve merge conflicts, I would start sweating.

Finding the Spark

Both VIM and Emacs are powerful and ubiquitous text editors and both are infamous for their steep learning curves. On my own, picking up such a tool was intimidating and frustrating. Here is what did the trick for me: watch a power user use them. It really hits you when this happens in person. I saw someone using org-mode in emacs, its table editor, exporting it in Markdown, HTML, and PDF, and then he used it to create a presentation using org-reveal, I was blown away 🤯. Later another friend of mine was using emacs and tramp to make code adjustments on a live server (avoid doing that) 🫡. During another pairing session, my colleague was using vim, navigating code, renaming variables with visual mode, and running macros-it was magic 🤹🏽. These moments made these editors cool for me-simple yet very pliable and that gave me enough escape velocity to push through the steep learning curve.

The Learning Curve

These editors are abstract tools that carry certain labels: "hard", "for smart people only", "set in their own ways". I struggled with two things when trying to pick them up. When I was working on a problem, I didn't want to get distracted by my editor, its mode, buffers, opening and closing etc. Second, I didn't consider myself smart and I kept my distance (thinking I was being mature) from tools that carried that impression.

But once I realized editors were a fundamental skill, I realized I should invest the time, don't make it (the editor) the last thing. I kept retrying, just like how I would approach a boss fight in a game. I didn't scare that easy in the next round, I noticed patterns, found my corner, got comfortable and started attacking. It grew on me. I acquired the taste. The same approach works for all crafts. Later, as I worked on new problem, these editors didn't get in the way-they provided the structure that will helped me focus.

I was lucky to work with such power users, and they allowed me the space to ask stupid questions. I still nag them about their setup when we meet in person. I use Emacs. I can't program without org-mode, magit, tramp et al. I am slowly working my way through its LSP support and configuring and tweaking things, one language at a time. I've tried other editors, I kept looking for these features and so far my attempts to install plugins/addons haven't worked. I keep returning to Emacs. As the landscape evolves with AI agents and MCP, I will explore whether I can integrate them with Emacs or if I'll need to adopt a more contemporary editor.

One Firmware for all ESP32 Variants: Solving Pin Mapping Pain

शांतनु — Sat, 16 Aug 2025 05:07:10 GMT

For my embedded project, I needed NFC card functionality for WiFi onboarding and user interactions. When integrating NFC functionality into ESP32 projects, pin mapping became a major pain point as I was working with different ESP32 boards.

Adafruit's arduino library example sets up the NFC reader in following manner:

#include <Wire.h>
// Using the SPI breakout, define the pins for SPI communication.
#define PN532_SCK  (2)
#define PN532_MOSI (3)
#define PN532_SS   (4)
#define PN532_MISO (5)
Adafruit_PN532 nfc(PN532_SCK, PN532_MISO, PN532_MOSI, PN532_SS);

These pins are placeholders and they would vary for each ESP32 variant and I had several: ESP-WROOM-32, ESP32-C3 Super Mini, S3, XIAO ESP32S3

I tested the reader across all these variants, different modes: SPI, I2C, wiring and reading different NFC cards.

First challenge was to figure out the mapping of pins. I found that espressif's arduino support is the best resource for it. For each board the file pins_arduino.h gives us the right pins. For the ESP32-C3 Super Mini board, the above example NFC reader code would become:

#include <Wire.h>
#define PN532_SCK  (4)
#define PN532_MOSI (6)
#define PN532_SS   (7)
#define PN532_MISO (5)
Adafruit_PN532 nfc(PN532_SCK, PN532_MISO, PN532_MOSI, PN532_SS);

But as I iterated through these ESP32 variants it became quite a pain adjusting those pins in the firmware and flashing it. Eventually I realized what would simplify this: I could have a single firmware that will work with everything:

#include <Wire.h>
Adafruit_PN532 nfc(SCK, MISO, MOSI, SS);

These pins, SCK, MISO are just like another constant: LED_BUILTIN, each Arduino board that doesn't use default pin 13, defines it in their pins_arduino.h header. Similarly all the variants have their own respective pins_arduino.h file with right pins. As I select the board inside Arduino IDE, these variables are always available. Further this pattern isn't limited to NFC readers, all the SPI peripheral using those pins would work.

CPR for a Docker container

शांतनु — Sat, 14 Jun 2025 10:35:55 GMT

Background

Picture this: You're experimenting with a Docker container, enable a feature, and suddenly your container is stuck in an endless restart loop. In a panic, you run docker compose down and watch everything disappear.

What You Should Do Instead

Don't lose the container, no matter how broken it is. Create a new image from the container using docker commit: docker commit <container-id> broken-image (you get container id using docker ps -a command)

From here there are a couple of things you could do. I was using Dockerfile to build and setup things. Modify it to use broken image as base and install the missing dependencies:

FROM broken-image:latest
RUN pip install <package-name>

And with this in place I can restart the docker compose stack.

Complicated changes

In case damage to your container is more severe there will be additional steps to revive the container.

Create image from your broken container: docker commit <container-id> broken-image
Create a new container from this broken image with a different entrypoint command (default command would restart the broken stack): docker run -it --entrypoint=/bin/bash broken-image:latest
Adjust or remove your changes, install missing dependencies, run migrations, what have you
Create a new image from this container that has all the fixes: docker commit <container-id-with-bash-running> fixed-image
Start a new container using this fixed-image and default command that brings up your original stack. In my case I removed build step from my docker-compose.yml file and pointed it to the new image:
```
   app:
     image: fixed-image:latest
```
Be careful with running faulty containers. I was really confused balancing docker compose commands and direct docker commands. I noticed that docker compose (re)start command would also (re)start all broken/existing containers and I had to manually remove them to be able to get the complete stack running again.

With this approach I was no longer building a new Docker image. Instead I used docker compose to start container using fixed-image and default command.

Summary:

Always test changes in development first
Use docker commit with your container before making risky changes

The right recipe

शांतनु — Fri, 30 May 2025 08:03:09 GMT

A colleague reached out to me for a pairing session on his project. I explained upfront that my hourly rate far exceeds most LLM subscription costs. He understood — while LLMs have their place, he needed help clarifying requirements and making real progress.

His existing setup: several machines pushing data to cloud, a looker studio dashboard connected to a placeholder google spreadsheet. To start, he wanted to make this dashboard live.

His requirements:

A live dashboard
Python based: his comfort zone
Daily data pulls: sufficient for non-temporal data

The solution was obvious, I have used it before: A GitHub action that runs daily, pulls cloud data and updates his spreadsheet — instantly making his dashboard live. I understand that I am contributing to the Github actions phenomena:

The trickiest parts? Wrestling with Google's Sheets API authentication and configuring GitHub secrets properly. But once those pieces clicked, everything flowed. Four one hour focused pairing sessions, that's it. He got a working solution plus he understood all the moving parts to continue experimenting on his own.

Four hours, serverless, an elegant solution. This is what going back to first principles looks like.

Setting Up Zephyr for ESP32: A Blinky LED Journey

शांतनु — Tue, 08 Apr 2025 11:49:10 GMT

I recently started working with a client on an ESP32 based project. Having prior experience with Zephyr on Nordic boards, I decided to leverage Zephyr's Espressif support for this project. While the documentation mentions the classic "blinky" example, I noticed it lacked the necessary device overlay file for my specific board.

Finding the Right Example

Fortunately, I discovered that the "PWM Blinky" example included sample overlay files I could reference. After compiling the example, I encountered this error when attempting to flash the device:

([Errno 5] could not open port /dev/ttyUSB0: [Errno 5] Input/output error: '/dev/ttyUSB0')

Running stat /dev/ttyUSB0 revealed that the device belonged to the dialout group. I fixed the permission issue by adding my user to this group:

sudo usermod -a -G dialout $USER

After rebooting to apply the new permissions, west flash worked perfectly.

Creating the missing overlay file

The basic Blinky documentation explains the need for an overlay file that points to the correct GPIO pin. Based on the PWM Blinky example, I discovered my board (esp32_devkitc_wroom) has an onboard blue LED connected to pwm_led_gpio0_2. I created following overlay file:

/ {
    aliases {
        led0 = &myled0;
    };
    leds {
        compatible = "gpio-leds";
        myled0: led_0 {
            gpios = <&gpio0 2 GPIO_ACTIVE_LOW>;
        };
    };
};

Success

With the overlay in place(samples/basic/blinky/boards/esp32_devkitc_wroom_procpu.overlay), I compiled the project and it worked:

west build -p always -b esp32_devkitc_wroom/esp32/procpu samples/basic/blinky

After flashing the board, there it was, blinking blue LED - a small victory that is still the first step and I keep revisiting it.

Next up: implementing the project's actual functionality, including WiFi provisioning, ePaper display integration, and LED ring controls.

Resolution / सलटारा

शांतनु — Fri, 08 Mar 2024 10:11:47 GMT

Continuing from the last post. The fact that Python interpreter didn't catch the regex pattern in tests but threw compile error on staging environment was very unsettling. Personally I knew that I am missing something on my part and I was very reluctant on blaming the language itself. Turns out, I was correct 🙈.

I was looking for early feedback and comments on the post and Punch was totally miffed by this inconsistency and specially the conclusion I was coming to

Umm, I'm not sure I'm happy with the suggestion that I should check every regex I write, with an external website tool to make sure the regex itself is a valid one. "Python interpreter ka kaam main karoon abhi?" :frown:

He quickly compared the behavior between JS(compiler complianed) and Python(did nothing). Now that I had full attention from him there was no more revisiting this at some later stage. We started digging. He confirmed that the regex failed with Python2 but not with Python3.11 with a simple command

docker run -it python:3.11 python -c 'import re; p = r"\s*+"; re.compile(p); print("yo")'

I followed up on this and that was the mistake on my part. My local python setup was 3.11, I was using this to run my tests and staging environment was using 3.10. When I ran my tests within containerized setup, similar to what we used on staging, Python interpreter rightly caught faulty regex:

re.error: multiple repeat at position 11

Something changed between python 3.11 and 3.10 release. I looked at the release logs and noticed this new feature atomic grouping and possessive quantifier. I am not sure how to use it or what it does 1. But with this feature, python 3.11 regex pattern: r"\s*+" is a valid one. I was using this to run tests locally. On staging we had python 3.10, and with it interpreter threw an error.

Lesson learned:

I was testing things by running things locally. Don't do that. Setup a stack and get is as close to the staging and production as possible. And always, always run tests within it.

You pull an end of a mingled yarn,

to sort it out,

looking for a resolution but there is none,

it is just layers and layers.

Assumptions / घारणा

शांतनु — Fri, 01 Mar 2024 10:09:24 GMT

In the team I started working with recently, I am advocating for code reviews, best practices, tests and using CI/CD. I feel in Python ecosystem it is hard to push reliable code without these practices.

I was assigned an issue to find features from text and had to extract money figures. I started searching for existing libraries (humanize, spacy, numerize, advertools, price-parser). These libraries always hit an edge case with my requirements. I drafted an OpenAI prompt and got a decent regex pattern that covered most of my requirements. I made a few improvements to the pattern and wrote unit and integration tests to confirm that the logic was covering everything I wanted. So far so good. I got the PR approved, merged and deployed. Only to find that the code didn't work and it was breaking on staging environment.

As the prevailing wisdom goes around regular expressions based on 1997 chestnut

Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.

I have avoided regular expressions, and here I am.

I was getting following stacktrace:

File "/lib/number_parser.py", line 19, in extract_numbers
pattern = re.compile("|".join(monetary_patterns))
File "/usr/local/lib/python3.10/re.py", line 251, in compile
return _compile(pattern, flags)
File "/usr/local/lib/python3.10/re.py", line 303, in _compile
p = sre_compile.compile(pattern, flags)
File "/usr/local/lib/python3.10/sre_compile.py", line 788, in compile
p = sre_parse.parse(p, flags)
File "/usr/local/lib/python3.10/sre_parse.py", line 955, in parse
p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0)
File "/usr/local/lib/python3.10/sre_parse.py", line 444, in _parse_sub
itemsappend(_parse(source, state, verbose, nested + 1,
File "/usr/local/lib/python3.10/sre_parse.py", line 672, in _parse
raise source.error("multiple repeat",	
re.error: multiple repeat at position 11

Very confusing. Seems there was an issue with my regex pattern. But the logic worked, I tested it. The pattern would fail for a certain type of input and work for others. What gives? I shared the regex pattern with a colleague and he promptly identified the issue, there was a redundant + in my pattern. I wanted to look for empty spaces and I had used a wrong pattern r'\s*+'.

I understand that Python is a interpreted and dynamically typed and that's why I wrote those tests(unit AND integration), containerized the application to avoid the wat. And here I was, despite all the measures, preaching best practices and still facing such a bug for the first time. I assumed that interpreter will do its job and complain about the buggy regex pattern and my tests would fail. Thanks to Punch we further dug into this behavior here.

A friend of mine, Tejaa had shared a regex resource: https://regex-vis.com/, it is a visual representation (state diagram of sorts) of the grammar. I tested my faulty regex pattern with \s*+ and the site reported: Error: nothing to repeat. This is better, error is similar with what I was noticing in my stack trace. I also tested the fixed pattern and the site showed a correct representation of what I wanted.

Always confirm your assumptions.

assumption is the mother of all mistakes (fuckups)

Pragmatic Zen of Python

शांतनु — Sat, 19 Aug 2023 06:57:14 GMT

I gave a talk at PyDelhi 2023 and got good feedback from the participants. It was a nice opportunity to meet lots of community member after a long time. These in person exchange of ideas and conversations are very essential for personal growth and learning. I will continue to do more in 2024 🤞🏾

2022....

शांतनु — Fri, 31 Dec 2021 18:07:55 GMT

Here is a wishlist for 2022. I have made similar lists in past, but privately. I didn't do well on following up on them. I want to change that. I will keep the list small and try to make them specific.

Read More

I didn't read much in 2021. I have three books right now with me: Selfish Gene by Richard dawkins, Snow Crash by Neal Stephenson, Release It! by Michael T. Nygard. I want to finish them. And possibly add couple more to this list. Last year, I got good feedback on how to improve and grow as a programmer. Keeping that in mind I will pick up some/a technical book. I have never tried before. Lets see how that goes.
Monitoring air quality data of Bikaner

When I was in Delhi back in 2014 I was really miffed by deteriorating air quality in Delhi. There was a number attached to it, AQI, it was registered by sensors in different locations. I felt it didn't reflect the real number of air quality for commuters like me. I would daily commute from office on foot and I would see lot of other folks stuck in traffic breathing in the same pollution. I tried to do something back then, didn't get too much momentum and stopped.

Recently with help of Shiv I am mentally getting ready to pick it up, again. In Bikaner we don't have official, public AQI number (1, 2, 3). I would like that to change. I want to start small, couple of boxes that could start collecting data. And add more features to it and increase the fleet to cover more areas in the City.
Write More:

I was really bad with writing things in 2021. Fix it. I want to write 4 to 5 good, thought out, well written posts. I also have lot of drafts, I want to finish writing them. I think being more consistent with writing club on wednesdays would be helpful.
Personal Archiving:

Again a long time simmering project. I want to put together scaffolding that can hold this. I recently read this post, the author talks about different services he runs on his server. I am getting a bit familiar with containers, docker-compose, ansible. And this post has given me some new inspirations on taking some small steps. I think the target around this project are still vague and not specific. I want some room here. To experiment, get comfortable, try existing tools.