In data import processes it’s often useful to have a “dry run” mode, that runs through the process but doesn’t actually save the data. This can allow you to check for validity and gather statistics, such as how many records already exist in the database. In this post, we’ll look at how to implement a dry run mode in Django by using a database transaction and rolling it back.
Python has no syntax to add type hints to lambdas, but that doesn’t mean you can’t use them in type-checked code. In this post we’ll look at how Mypy can infer the types for lambdas, based on where they’re used.
You want to pass your data from your Django view to JavaScript, in your template. And, you want to do it securely, with no risk of accidentally allowing malicious code injection. Great, this is the post for you!
Hynek Schlawack recently described graduality as Python’s super power: the ability to prototype in the REPL, and gradually add linting, type checking, and other practices to refine your code into maintainable, production-ready software. You can also apply graduality within tools, activating checks one at a time and fixing the resulting errors as you go.
partial() with transaction.on_commit() to avoid late-binding bugsDjango’s transaction.on_commit() allows you to run a function after the current database transaction is committed. This is useful to ensure that actions with external services, like sending emails, don’t run until the relevant data is definitely saved.
Normally your Django project’s deploy process runs the migrate command, and that takes care of updating your database as necessary. Especially on smaller databases, Django’s migration system can “just do it” for you.
Python’s requests package is very popular. Even if you don’t use it directly, it’s highly likely one of your dependencies does.
Slow queries happen, and when they do, it can be tough to dissect why they’re slow. This difficulty is compounded by using Django’s ORM, since it generates the SQL for you, so you may have little idea of the actual queries “under the hood”.
Investigating flaky tests is a dull necessity of testing. At least it is (in the best case) infrequent. Here are some shell commands you can use to automate steps in your investigations. These will work on (at least) bash and zsh.
Your PostgreSQL server is seizing up, with some naughty queries consuming too many resources or blocking others. Don’t panic! You can stop those problem queries and stabilize your system.
In a 2019 talk/rant titled “Everyone Watching This Is Fired”, games industry veteran Mike Acton rattled off a sample of 50 things he expects of developers he works with. The title refers to his tongue-in-cheek suggestion that anyone who doesn’t meet all these requirements would be immediately fired.
Projects often accumulate an amount of unused code. This cruft makes a prjoect harder to navigate, and can confuse future development or debugging.
HTCPCP, or Hyper Text Coffee Pot Control Protocol, was published as an April Fool’s joke 24 years ago today. It’s an HTTP extension for controlling coffee pots, and whilst it is a joke, it appears in various places around the web.
It’s all too easy to forget to pass a variable to your template or make a typo in a variable name. Unfortunately, it can be quite hard to debug such mistakes, since Django’s default behaviour is to ignore the problem and render an empty string.
get_user_model()Django’s authentication system, django.contrib.auth, provides a built-in User model class. You can swap this to a different class with the AUTH_USER_MODEL setting, most easily at the start of the project.
It’s a good idea to ensure your project uses the same Node.js version in all environments. This way you can be sure that your code will work as expected, from development to production.
--keep-baseWhen you have a long-lived feature branch with many “work in progress“ commits, it can become tiresome to rebase it onto your main branch due to conflicts. You can end up fixing conflicts in the same areas of the same files over and over for multiple commits.
Occasionally it’s useful to run commands on all files in your repository, or those matching a pattern. This is possible by combining git ls-files and xargs.
I’ve just released django-htmx 1.9.0. As part of this release, it now has a documentation site built with Sphinx, hosted on Read the Docs at django-htmx.readthedocs.io.
WhiteNoise is a simple solution to serving static assets. It lets you skip configuring a separate web server for your static assets, and serve them straight from Django. It’s a brilliant tool. I’ve used it for years on various projects, and I’ve recommended it many times, and mentioned it in several blog posts.
I joined host Tobias Macey on Podcast.__init__, in Episode 349, published this monday. The episode is titled “Improve Your Productivity By Investing In Developer Experience Design For Your Projects”. We covered various topics related to “developer experience” and general ways to improve it on any Python project.
contrib.staticfilesSource maps are files that map your minified CSS or JavaScript back to the original code. They allow you to use your browser’s development tools to debug minified code as if it were the original. Also some error capture tools, such as Sentry, can use source maps to report errors for the original code.
Here’s a small problem I’ve seen where several modules share versions of the same “constant” variable. It came up in the context of a Django project with multiple settings files, but it could happen in different contexts.
PNGs can be losslessly optimized to reduce their file size, by picking a better compression algorithm for the given image. The savings can be significant, like 50% (especially for macOS screenshots). This is an easy way to make web sites load faster.
In December I was awarded the Malcolm Tredinnick Award. This is an annual award, selected by nominations from anyone in the Django community. I’m incredibly honoured to have been selected, joining a fine list of past recipients. I’ve been inspired by every one of them.