Posts tagged: python

All posts with the tag "python"

275 posts latest post 2026-03-31
Publishing rhythm
Feb 2026 | 1 posts
Copier Tasks | Python templating post run task

Copier allows you to run post render tasks, just like cookiecutter. These are defined as a list of tasks in your copier.yml. They are simply shell commands to run.

The example I have below runs an update-gratitude bash script after the copier template has been rendered.

# copier.yml num: 128 _answers_file: .gratitude-copier-answers.yml _tasks: - "update-gratitude"

I have put the script in ~/.local/bin so that I know it’s always on my $PATH. It will reach back into the copier.yml and update the default number.

Gradual Typing in Python

I’ve referenced a video from Anthony Sotile in passing conversation several times. Walking through his gradual typing process has really helped me understand typing better, and has helped me make some projects better over time rather than getting slammed with typing errors.

https://youtu.be/Rk-Y71P_9KE

Run Mypy as is, don’t get fancy yet. This will not reach into any functions unless they are alreay explicitly typed. It will not enforce you to type them either.

pip install mypy mypy . # or your specific project to avoid .venvs mypy src # or a single file mypy my-script.py

Step 2 #

Next we will add check-untyped-defs, this will start checking inside functions that are not typed. To add this to your config create a setup.cfg with the following.

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Python Reverse Sluggify

In order to make an auto title plugin for markata I needed to come up with a way to reverse the slug of a post to create a title for one that does not explicitly have a title.

Here I have a path available that gives me the articles path, ex. python-reverse-sluggify.md. An easy way to get rid of the file extension, is to pass it into pathlib.Path and ask for the stem, which returns python-reverse-sluggify. Then from There I chose to replace - and _ with a space.

article["title"] = ( Path(article["path"]).stem.replace("-", " ").replace("_", " ").title() )

To turn this into a markata plugin I put it into a pre_render hook.

Get Python docstring with ast

Getting docstrings from python’s ast is far simpler and more reliable than any method of regex or brute force searching. It’s also much less intimidating than I originally thought.

First you need to load in some python code as a string, and parse it with ast.parse. This gives you a tree like object, like an html dom.

py_file = Path("plugins/auto_publish.py") raw_tree = py_file.read_text() tree = ast.parse(raw_tree)

Getting the Docstring #

You can then use ast.get_docstring to get the docstring of the node you are currently looking at. In the case of freshly loading in a file, this will be the module level doctring that is at the very top of a file.

module_docstring = ast.get_docstring(tree)

Walking for all functions

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Python Respect the .gitignore

Many tools such as ripgrep respect the .gitignore file in the directory it’s searching in. This helps make it incredibly faster and generally more intuitive for the user as it just searches files that are part of thier project and not things like their virtual environments, node modules, or compiled builds.

Editors like vscode often do not include files that are .gitignored in their search either.

pathspec is a pattern matching library that implements git’s wildmatch pattern so that you can ignore files included in your .gitignore patterns. You might want this to help make your libraries more performant, or more intuitive for you users.

import pathspec from pathlib import Path markdown_files = Path().glob('**/*.md') if (Path(".gitignore").exists(): lines = Path(".gitignore").read_text().splitlines() spec = pathspec.PathSpec.from_lines("gitwildmatch", lines) markdown_files = [ file for file in...

Rename Python Variables with nvim

I don’t use refactoring tools as much as I probably should. mostly because I work with small functions with unique names, but I recently had a case where a variable name m was everywhere and I wanted it named better. This was not possible with find and replace, because there were other m’s in this region.

I first tried the nvim lsp rename, and it failed, Then I pip installed rope, a refactoring tool for python, and it just worked!

pip install rope

Once you have rope installed you can call rename on the variable.

Python Find Available Port

When running a python process that requires a port it’s handy if there is an option for it to just run on the next avaialble port. To do this we can use the socket module to determine if the port is in use or not before starting our process.

python functools total ordering

functools.total_ordering makes adding all of six of the rich comparison operators to your custom classes much easier, and more likely that you remember all of them.

From the Docs: The class must define one of __lt__(), __le__(), __gt__(), or __ge__ In addition, the class should supply an __eq__() method.

one of these

and required to have this one

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Implement --pdb in a python cli

Adding a --pdb flag to your applications can make them much easier for those using it to debug your application, especially if your applicatoin is a cli application where the user has much fewer options to start this for themselves. To add a pdb flag --pdb to your applications you will need to wrap your function call in a try/except, and start a post_mortem debugger. I give credit to this stack overflow post for helping me figure this out.

Python Enum

Python comes with an enum module for creating enums. You can make your own enum by inheriting importing and inheriting from Enum.

from enum import Enum class LifeCycle(Enum): configure = 1 glob = 2 pre_render = 3 render = 4 post_render = 5 save = 6

auto incrementing #

Enum values can be auto incremented by importing auto, and calling auto() as their value.

from enum import Enum, auto class LifeCycle(Enum): configure = auto() glob = auto() pre_render = auto() render = auto() post_render = auto() save = auto()

using the enum #

Enum’s are accessed directy under the class itself, and have primarily two methods underneath each thing you make, .name and .value.

Installing Pipx on Ubuntu

I recently paired up with another dev running windows with Ubuntu running in wsl, and we had a bit of a stuggle to get our project off the ground because they were missing com system dependencies to get going.

Open up a terminal and get your required system dependencies using the apt package manager and the standard ubuntu repos.

sudo apt update sudo apt upgrade sudo apt install \ python3-dev \ python3-pip \ python3-venv \ python3-virtualenv pip install pipx

Using an Ansible-Playbook #

I like running things like this through an ansible-playbook as it give me some extra control and repeatability next time I have a new machine to setup.

- hosts: localhost gather_facts: true become: true become_user: "{{ lookup('env', 'USER') }}" pre_tasks: - name: update repositories apt: update_cache=yes become_user: root changed_when: False vars: user: "{{ ansible_user_id }}" tasks: - name: Install System Packages 1 (terminal) become_user: root apt: name: - build-essential - python3-dev - python3-pip - python3-venv - python3-virtualenv -...

Using Copier Answers to rerun templates quickly

The copier answers file is a key component to making your templates re-runnable. Let’s look at the example for my setup.py.

❯ tree ~/.copier-templates/setup.py /home/walkers/.copier-templates/setup.py ├── [[ _copier_conf.answers_file ]].tmpl ├── copier.yml ├── setup.cfg └── setup.py.tmpl 0 directories, 4 files

Inside of my [[ _copier_conf.answers_file ]].tmpl file is this, a message not to muck around with it, and the ansers in yaml form. The first line is just a helper for the blog post.

# ~/.copier-templates/setup.py/\[\[\ _copier_conf.answers_file\ \]\].tmpl # Changes here will be overwritten by Copier; NEVER EDIT MANUALLY [[_copier_answers|to_nice_yaml]]

Inside my copier.yml I have setup my _answers_file to point to a special file. This is because this is not a whole projet template, but one just for a single file.

# copier.yml # ... _answers_file: .setup-py-copier-answers.yml

Once I change the _answers_file I was incredibly stuck

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Making a Textual Widget from a Rich Renderable

Once you have made your sick looking cli apps with rich, eventually you are going to want to add some keybindings to them. Currently Textual, also written by @willmcgugan, does this extremely well. Fair Warning it is in super beta mode and expected to change a bunch. So take it easy with hopping on the train so fast.

Install them from the command line.

pip install textual pip install rich

Import make a .py file and import them in it.

from textual.app import App from textual.widget import Widget from rich.panel import Panel

Make what you have a widget #

If you return your rich renderable out of...

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pipx examples

count lines of code # pipx run pygount markata pipx run pygount markata --format=summary pipx run pygount markata --suffix=cfg,py,yml
Changing copier template strings (_endops)

I was completely stuck for awhile. copier was not replacing my template variables. I found out that adding all these _endops fixed it. Now It will support all of these types of variable wrappers

# copier.yml _templates_suffix: .jinja _envops: block_end_string: "%}" block_start_string: "{%" comment_end_string: "#}" comment_start_string: "{#" keep_trailing_newline: true variable_end_string: "}}" variable_start_string: "{{"

!RTFM: Later I read the docs and realized that copier defaults to using [[ and ]] for its templates unlike other tools like cookiecutter.

copier template variables

I’ve been looking for a templating tool for awhile that works well with single files. My go to templating tool cookiecutter does not work for single files, it needs to put files into a directory underneath of it.

By default copier uses double square brackets for its variables. variables in files, directory_names, or file_names will be substituted for their value once you render them.

# hello-py/hello.py.tmpl print('hello-[[name]]')

note! by default copier will not inject variables into your template-strings unless you use a .tmpl suffix.

Before running copier we need to tell copier what variables to ask for, we do this with a copier.yml file.

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Running Kedro on Ubuntu 21.10 Impish Indri

I just installed a brand new Ubuntu 21.10 Impish Indri, and wanted a kedro project to play with so I did what any good kedroid would do, I went to my command line and ran

pipx run kedro new --starter spaceflights

But what I got back was not what I expected!

Fatal error from pip prevented installation. Full pip output in file: /home/walkers/.local/pipx/logs/cmd_2022-01-01_20.42.16_pip_errors.log Some possibly relevant errors from pip install: ERROR: Could not find a version that satisfies the requirement kedro (from versions: none) ERROR: No matching distribution found for kedro Error installing kedro.

This is weird, why cant I run kedro new with pipx? Lets try pip.

pip install kedro

Same issue.

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A Minimal Pluggy Example

Pluggy makes it so easy to allow users to modify the behavior of a framework without thier specific feature needing to be implemented in the framework itself.

I’ve really been loving the workflow of frameworks built with pluggy. The first one that many python devs have experience with is pytest. I’ve never created a pytest plugin, and honestly at the time I looked into how they were made was a long time ago and it went over my head. I use a data pipelining framework called kedro, and have build many plugins for it.

super easy to do

As long as the framework document the hooks that are available and what it passes to them it’s so easy to make a plugin. Its just importing the hook_impl, making a class with a function that represents one of the hooks, and decorating it.

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My first impressions with pyenv

pyenv provides an easy way to install almost any version of python from a large list of distributions. I have simply been using the version of python from the os package manager for awhile, but recently I bumped my home system to Ubuntu 21.10 impish, and it is only 3.9+ while the libraries I needed were only compatable with up to 3.8.

I needed to install an older version of python on ubuntu

I’ve been wanting to check out pyenv for awhile now, but without a burning need to do so.

Based on the Readme it looked like I needed to install using homebrew,so this is what I did, but I later realized that there is a pyenv-installer repo that may have saved me this need.

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