emrox's blurblog

To Sleep, Perchance… by Doug
Thursday April 24^th, 2025 at 4:26 AM

Savage Chickens – Cartoons on Sticky Notes by Doug Savage

To Sleep, Perchance...

Happy belated birthday, Shakespeare.

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emrox

25 minutes ago

Hamburg, Germany

Creating CSS Theme Variables from a JS file
Thursday April 24^th, 2025 at 4:24 AM

CSS In Real Life

For many projects I work on it’s useful to define all of our brand colours in a JavaScript file, particularly as I work on a lot of data visualisations that use them. Here’s an abridged example of how I define brand colours, as well as those used for data visualisations, and their variants:

// theme.js
const theme = {
  color: {
    brand: {
      primary: {
        DEFAULT: '#7B1FA2',
        light: '#BA68C8',
        dark: '#4A148C',
      },
      secondary: {
        DEFAULT: '#E91E63',
        light: '#F48FB1',
        dark: '#C2185B',
      },
    },
    data: {
      blue: '#40C4FF',
      turquoise: '#84FFFF',
      mint: '#64FFDA',
    },
  },
}

I also need those variables in my CSS, where they’re defined as custom properties. But I don’t want to have to maintain my colour theme in two places! That’s why I created a script to create a CSS file that defines custom properties from a JS source file. If you’re interested, here’s how it’s done.

Setup

For this walkthrough you’ll need Node and NPM installed. If you’re already familiar with setting up a project using NPM, you can skip over this part. Otherwise, assuming you’ve already installed NPM globally, you’ll need to run npm init in your project root and follow the prompts. This creates a package.json file in the root of your project directory.

Create a script file

We’ll need to create a JS file for our script so we can run it from the command line. For simplicity, let’s create a file called index.js in the project root, and add a single line:

// index.js
console.log('Hello world')

Now we should be able to run node index.js from the terminal and see our “Hello world” message, so we know our very basic script has run successfully.

Import the theme

Now let’s import the theme defined in the JS file from which we want to create our CSS custom properties. We’ll call this theme.js. You’ll need to make sure your file exports the theme so it can be imported elsewhere.

// theme.js

const theme = {
  // Theme colours as defined above...
}

export default theme

// index.js
import theme from './theme.js'

console.log(theme)

Running the script again with node index.js, we should see the theme object logged in the terminal. Now we need to actually do something with it!

Input and output

The aim here is to create CSS custom properties that correspond to the theme object keys. For example:

// theme.js
const theme = {
  color: {
    primary: 'red',
    secondary: 'blue',
  },
}

Would become:

/* styles.css */
:root {
  --color-primary: red;
  --color-secondary: blue;
}

However, our theme as defined in our JS file isn’t quite so simple. As you can see from the example at the beginning, some of our colour definitions include multiple lighter or darker variants, nested more than one level deep.

What we would like here is to map our colours so that their custom property names are prefixed with their ancestor property names. For example, we would use --color-brand-primary for the default primary brand colour, and --color-brand-primary-light for its lighter variant.

:root {
  --color-brand-primary: #7b1fa2;
  --color-brand-primary-light: #ba68c8;
}

We shouldn’t assume that all colour will have the same property names either. We should be able to define them using any names we like, as many levels as is required.

Note, I’m including color here as a property of theme. That’s because the actual theme configuration might include things like font families too. We’ll keep it simple and focus on colour here, but the script we’re going to write should (theoretically!) work for any object properties of the theme.

Writing a recursive function

We’ll write a function that looks at any key/value pair and returns the CSS custom property definition as a string.

The first part is easy enough:

// index.js
import theme from './theme.js'

const mapTheme = ([key, value]) => {
  // If value is a string, return the result
  if (typeof value === 'string') {
    return `--${key}: ${value}`
  }
}

This would work fine is we had a very simple theme, like this:

const theme = {
  purple: '#7B1FA2',
  pink: '#E91E63',
}

We could convert our theme object to an array using Object.entries() and map over the entries with this function:

// index.js
import theme from './theme.js'

const mapTheme = ([key, value]) => {
  // If value is a string, return the result
  if (typeof value === 'string') {
    return `--${key}: ${value}`
  }
}

console.log(Object.entries(theme).map(mapTheme))
// result: ['--purple: #7B1FA2', '--pink: #E91E63']

However, that’s not going to be enough for our nested theme variables. Instead we’ll amend the mapTheme() function so that if the value is not a string

//index.js
const mapTheme = ([key, value]) => {
  // If value is a string, return the result
  if (typeof value === 'string') {
    return `--${key}: ${value}`
  }

  // Otherwise, call the function again to check the next pair
  return Object.entries(value).flatMap(mapTheme)
}

console.log(Object.entries(theme).flatMap(mapTheme))

You might notice we’re using the flatMap() array method instead of map() as above. This is so that the result is output as a flat array, which is what we want, instead of nesting the custom properties.

If we check the result at this point, we’ll see it’s not quite what we want. We end up with custom property names that correspond to the nested object keys but don’t tell us anything about the parent groups. We also end up with duplicates:

[
  '--DEFAULT: #7B1FA2',
  '--light: #BA68C8',
  '--dark: #4A148C',
  '--DEFAULT: #E91E63',
  '--light: #F48FB1',
  '--dark: #C2185B',
  '--blue: #40C4FF',
  '--turquoise: #84FFFF',
  '--mint: #64FFDA',
]

If we want more useful custom property names we’ll need to append the name to its parent group name, unless the key is DEFAULT, in which case we’ll simply return the parent group key.

// index.js
import theme from './theme.js'

const mapTheme = ([key, value]) => {
  // If value is a string, return the result
  if (typeof value === 'string') {
    return `--${key}: ${value}`
  }

  return Object.entries(value).flatMap(([nestedKey, nestedValue]) => {
    // Append to the custom property name, unless default value
    const newKey = nestedKey === 'DEFAULT' ? key : `${key}-${nestedKey}`

    // Check the new key/value pair
    return mapTheme([newKey, nestedValue])
  })
}

console.log(Object.entries(theme).flatMap(mapTheme))

This results in far more helpful names:

[
  '--color-brand-primary: #7B1FA2',
  '--color-brand-primary-light: #BA68C8',
  '--color-brand-primary-dark: #4A148C',
  '--color-brand-secondary: #E91E63',
  '--color-brand-secondary-light: #F48FB1',
  '--color-brand-secondary-dark: #C2185B',
  '--color-data-blue: #40C4FF',
  '--color-data-turquoise: #84FFFF',
  '--color-data-mint: #64FFDA',
]

Codepen example

An alternative with a `for` loop

By the way, we could do this in a slightly different way with a for loop. It’s a similar amount of code, but we don’t need the nested flatMap, which might make for a slightly more elegant solution (you be the judge!):

// index.js
let result = []

const mapTheme = (obj, key = null) => {
  for (const property in obj) {
    let name = key || property

    if (property !== 'DEFAULT' && !!key) {
      name = `${key}-${property}`
    }

    if (typeof obj[property] === 'string') {
      result.push(`--${name}: ${obj[property]}`)
    } else {
      mapTheme(obj[property], name)
    }
  }
}

mapTheme(theme)

console.log(result)

Codepen example

Writing to a file

Now we can take these values and write them to a CSS file for use in our project. We could simply copy them from the console, but even better if we write a script that will do it for us.

We’ll import the writeFile method from the Node JS library and write a new async function called buildTheme, which we’ll export. (We’ll remove the console log from the previous example.)

// index.js
import { writeFile } from 'fs/promises'
import theme from './theme.js'

const mapTheme = ([key, value]) => {
  /* ... */
}

const buildTheme = async () => {
  try {
    console.log(Object.entries(theme).flatMap(mapTheme))
  } catch (e) {
    console.error(e)
  }
}

buildTheme()

We should now be able to run the script from the command line by typing node index.js and see the result logged.

Next we’ll convert the custom properties into a suitable format for our CSS file. We’ll want each custom property to be indented and set on its own line, which we can do with the escaped characters \n and \t respectively.

// index.js
import { writeFile } from 'fs/promises'
import theme from './theme.js'

const mapTheme = ([key, value]) => {
  /* ... */
}

const buildTheme = async () => {
  try {
    const result = Object.entries(theme).flatMap(mapTheme)

    // Indent each custom property and append a semicolon
    let content = result.map((line) => `\t${line};`)

    // Append and prepend brackets, and put each item on a new line
    content = [':root {', ...content, '}'].join('\n')

    console.log(content)
  } catch (e) {
    console.error(e)
  }
}

buildTheme()

All that remains is to write the result to a CSS file, using the writeFile() method. We’ll need to specify the location of the file we want to write to, and its character encoding, which will be 'utf-8'. We’re including a helpful console log informing the user that the file has been written, and ensuring we catch any errors by also logging them to the console.

// index.js
import { writeFile } from 'fs/promises'
import theme from './theme.js'

const mapTheme = ([key, value]) => {
  /* ... */
}

const buildTheme = async () => {
  try {
    const result = Object.entries(theme).flatMap(mapTheme)

    let content = result.map((line) => `\t${line};`)
    content = [':root {', ...content, '}'].join('\n')

    // Write to the file
    await writeFile('src/theme.css', content, { encoding: 'utf-8' })

    console.log('CSS file written')
  } catch (e) {
    console.error(e)
  }
}

buildTheme()

Running the script now outputs the CSS file we need.

@theme {
  --color-brand-primary: #7b1fa2;
  --color-brand-primary-light: #ba68c8;
  --color-brand-primary-dark: #4a148c;
  --color-brand-secondary: #e91e63;
  --color-brand-secondary-light: #f48fb1;
  --color-brand-secondary-dark: #c2185b;
  --color-data-blue: #40c4ff;
  --color-data-turquoise: #84ffff;
  --color-data-mint: #64ffda;
}

Here’s the complete file:

// index.js
import { writeFile } from 'fs/promises'
import theme from './theme.js'

const mapTheme = ([key, value]) => {
  if (typeof value === 'string') {
    return `--${key}: ${value}`
  }

  return Object.entries(value).flatMap(([nestedKey, nestedValue]) => {
    const newKey = nestedKey === 'DEFAULT' ? key : `${key}-${nestedKey}`

    return mapTheme([newKey, nestedValue])
  })
}

const buildTheme = async () => {
  try {
    const result = Object.entries(theme).flatMap(mapTheme)

    let content = result.map((line) => `\t${line};`)
    content = [':root {', ...content, '}'].join('\n')

    await writeFile('src/theme.css', content, { encoding: 'utf-8' })

    console.log('CSS file written')
  } catch (e) {
    console.error(e)
  }
}

buildTheme()

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emrox

27 minutes ago

Hamburg, Germany

Geocoding APIs compared: Pricing, free tiers & terms of use
Wednesday April 23^rd, 2025 at 8:28 AM

bit off

Author's note

This article was originally published on Superface blog before the pivot to agentic tooling platform and is republished here with company's permission.

I am no longer working with geocoding APIs and the content of this article may be outdated.

Geocoding is the process of converting an address to geolocation coordinates (latitude and longitude). Reverse geocoding is the opposite: assigning a street address to the given coordinates. Examples of geocoding include:

Obvious ones, like finding a location on a map or displaying an address of a selected location.
Visualization of customer data.
Working with coordinates stored in photos.
Local search, such as displaying events or restaurants in the user’s proximity or within a city radius.

How do you build this feature? The easiest way is to use a geocoding API, which often includes reverse geocoding and address data cleaning functions as well.

The good news is that there isn’t a shortage of geocoding API providers to choose from. The bad news is that you have to pick one. Which is why we’re here: to help you decide on the most suitable geocoding API for your project.

Comparison criteria

In this article, we will look at the pricing model, and terms of use:

Pricing: Most geocoding API providers have a volume-based pricing. So, we will look at pricing tiers and price per API request.
Free tier: Typically there is a free or trial tier with a limited number of requests or limited functionality. This can be useful for testing the API or even keeping your costs low for personal or low-budget projects.
Data terms of use: It’s essential to know if there are any limitations about the data usage: Does the provider require displaying an attribution? Is it even okay to use the data for commercial use?

In the follow-up articles, we will also explore additional criteria:

Accuracy: It doesn’t matter whether the API is cheap if the results are useless. So, we will do a head-to-head comparison of various queries and compare the results.
Performance: If your project requires displaying the geocoding results in real-time, then every millisecond matters.

What’s Superface and why is this comparison neutral

At Superface we don’t provide a geocoding API. Instead, we are building a universal API client which lets you connect to any API and any provider – directly from your application without passing the data through our servers. You can even use multiple providers behind a single interface without the need to study the documentation for each or keep up with the API changes.

Geocoding is particularly one domain where your project can benefit from using multiple API providers. Whether it’s for accuracy, cost management, or legal reasons. Our goal is to provide you with accurate and impartial information about geocoding APIs, and we will show you how you can use them immediately with OneSDK, our API client.

Oh, and one more thing: OneSDK is free and open-source, it doesn’t matter whether you will use it for geocoding twice or a billion times. Our business is built around providing the connectors to the APIs and their long-term support, but not around the usage volume.

Provider	Free Requests	Rate Limit (requests per second)	Pricing (per 1,000 requests)	Additional Notes
HERE	30,000/month	5	$0.83 up to 5M $0.66 up to 10M
Google Maps	40,000/month ($200 credit)	50	$5 up to 100,000 $4 up to 500,000	Attribution & Google Maps required
Azure Maps	5,000/month	500 (geocoding) 250 (reverse geocoding)	$4.50
OpenCage	2,500/day	1 (free) 15 (X-Small) up to 40 (Large)	$0.17 (10,000 per day) $0.11 (300,000 per day)^[1]	Free trial for testing only Monthly fixed pricing
TomTom Maps	2,500/day	5	$0.54
LocationIQ	5,000/day	2	$0.16 (10,000 per day) $0.03 (1M per day)^[1:1]	Free plan requires attribution Monthly fixed pricing
Nominatim	n/a	1	n/a	Low-volume, noncommercial use only Attribution required

HERE

HERE’s pricing starts with the Limited Plan, which provides you with 1,000 free requests per day, with a rate limit of 5 requests per second.

If you provide payment information, you are upgraded to the Base Plan. The Base Plan removes the rate limit and sets you up for 30,000 free requests per month. Above that, requests up to 5 million are $0.830 per 1,000, and $0.660 per 1,000 requests between 5 and 10 million per month.

Google Maps Platform

Google Maps Platform requires you to provide billing details to use the Geocoding API, and provides you with $200 of free credit per month, which is good for 40,000 free geocoding API requests (check the Geocoding API Usage and Billing).

If that’s not enough, the pricing starts at $5 per 1,000 requests up to 100,000 requests per month. Above that, the price gets lower to $4 per 1,000 requests up to 500,000 requests.

Regardless of usage, there’s a rate limit of 50 requests per second. Google also prohibits displaying of geocoding results on another map than Google Maps, and requires displaying Google logo for attribution.

Azure Maps

Azure Maps provides 5,000 free requests per month (see the pricing for Azure Maps Search), and the price per 1,000 requests above that is $4.50 (up to 500,000 requests).

Queries are rate limited to 500 per second for geocoding, and 250 per second for reverse geocoding.

OpenCage

OpenCage pricing is richer than for other services. You have a choice of purchasing a one-time requests package (valid up to one year), or subscribing to different usage tiers on a monthly or annual basis.

The free tier is intended only for testing and development and provides you with 2,500 requests per day, rate limited to 1 request per second. The cheapest package costs $50 per month and comes with 10,000 requests per day (about $0.17 per 1,000 requests) and a rate limit of 15 requests per second. The biggest pre-Enterprise package costs $1,000 per month, with 300,000 requests per day and a rate limit of 40 requests per second (which is approx $0.11 per 1,000 requests).

One nice thing is that the daily request limit is “soft” – if you occasionally cross the limit, the service won’t be blocked, and you won’t be charged anything extra. Only if you repeatedly pass the limit OpenCage asks you to upgrade your plan for the next month.

LocationIQ

LocationIQ pricing is very similar to OpenCage's. You have a choice of plans paid on a monthly and annual basis, but no option to purchase a one-time requests package.

The free tier does allow commercial usage as long as you include a link in your application to LocationIQ. Furthermore, the free tier limit is doubled compared to OpenCage, with 5,000 free requests allowed per day and a rate limit of 2 requests per second. The smallest package is basically the same as OpenCage's: it costs $49 per month and comes with 10,000 requests per day (about $0.16 per 1,000 requests) and a rate limit of 15 requests per second. However, the biggest package includes 1 million requests per day for $950 per month (about $0.03 per 1,000 requests).

Similar to OpenCage, LocationIQ has a “soft” limit for daily requests, allowing requests “upto an additional 100% of your daily limit”. For example, on the smallest package, you can occasionally perform 20,000 requests per day before getting an error.

TomTom Maps API

TomTom provides a generous free tier with 2,500 requests per day available for commercial applications as well. Above that, 1,000 requests cost €0.50 ($0.54).

Nominatim

Nominatim is a bit different from the other services on this list. It’s primarily an open-source project that uses data from OpenStreetMap. And conversely, OpenStreetMap’s search is powered by Nominatim. You can (and should) run Nominatim on your server, but if you just want to try the API or have a low-volume hobby project, you’re welcome to use the Nominatim instance provided by OpenStreetMap.

However, pay close attention to its usage policy, in particular:

Maximum of 1 request per second.
Identify your application using User-Agent or HTTP Referer headers.
Display attribution.
Don’t resell the data.

Nominatim is also used by some commercial providers, including OpenCage and LocationIQ.

Pricing comparison

While each service has different pricing tiers, we can compare the price based on the number of requests made. We’ve omitted Nominatim in this comparison, since it’s always free, but isn’t intended for commercial projects.

Small usage (up to 30,000 requests / month)

HERE: free
Google Maps Platform: free (with credit)
Azure Maps: $112.5/month
OpenCage: free or $50/month (X-Small)
TomTom Maps: free
LocationIQ: free or $49/month (Geocoding Lite)

Medium usage (100,000 requests/month or 3,333/day)

HERE: $58.1
Google Maps Platform: $300 (with credit)
Azure Maps: $427.5
OpenCage: $50 (X-Small)
TomTom Maps: $16.2 ($0.54/day)
LocationIQ: free or $49/month (Geocoding Lite)

High usage (300,000 requests/month or 10,000/day)

HERE: $224.1
Google Maps Platform: $1,100 (with credit)
Azure Maps: $1327.5
OpenCage: $50 (X-Small) or $125 (Small)
TomTom Maps: $121.5 ($4.05/day)
LocationIQ: $49/month (Geocoding Lite) or $99 (Developer)

Conclusion: What’s the best geocoding API deal?

Based purely on pricing, we can draw a conclusion about each provider.

Azure Maps is, for higher volume scenarios, the most expensive option, with low free tier and fixed price per request. Similar to Google Maps, Azure Maps’ price per 1,000 requests is almost ten times higher compared to other providers.

Google Maps Platform is similarly expensive, but also the most restrictive provider, with requirements for attribution and displaying data using their embedded maps. This can introduce additional costs, as Google Maps with JavaScript API is also paid per usage.

OpenCage and LocationIQ both provide monthly plans with a fixed price. OpenCage also provides the possibility to purchase one-off usage credits and handles billing in multiple currencies automatically. LocationIQ, on the other hand, provides more generous free tier, and their monthly plans are cheaper, especially for higher volume usage. The “Business Plus” plan in particular allows for 1 million requests per day, allowing for a whopping 30 million requests per month without negotiating custom pricing. A monthly subscription probably makes the most sense if your usage volume of the geocoding API is consistent throughout the month.

On the other hand, TomTom Maps may be preferable if your usage is uneven. The price per 1,000 calls is among the lowest, and you have a large amount of free requests per day. And unlike OpenCage and LocationIQ, you don't need to pay a monthly subscription. The commercial-friendly free tier is also a great option for smaller and low-budget projects.

HERE is a viable option for high-volume usage. While most providers require you to upgrade to the (presumably expensive) Enterprise plan once you use around 500,000 requests/month, HERE will ask you only once you reach 10 million monthly requests. (However, LocationIQ allows for 1 million requests per day with their biggest package.)

Finally, Nominatim is a special option. Great for small projects, but not intended for commercial usage. Still, if you use the service, consider supporting the project.

Resources

OpenCage has a detailed guide on comparing and testing geocoding providers; rather than comparing individual providers, it explains what criteria you should consider.
On GIS Stack Exchange, you can find a sheet with a comprehensive comparison of providers’ accuracy; the last update was in 2021.
You can find additional comparisons by Smarty (formerly SmartyStreets), Geoapify, and Geocodio, however some information about pricing may be outdated and the comparisons are obviously biased.

Updates

The article was updated on June 26, 2023, to include LocationIQ per the provider's request.

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emrox

20 hours ago

Hamburg, Germany

Some Advanced Python Features
Wednesday April 23^rd, 2025 at 6:06 AM

Python is one of the most widely adopted programming languages in the world. Yet, because of it’s ease and simplicity to just “get something working”, it’s also one of the most underappreciated.

If you search for Top 10 Advanced Python Tricks on Google or any other search engine, you’ll find tons of blogs or LinkedIn articles going over trivial (but still useful) things like generators or tuples.

However, as someone who’s written Python for the past 12 years, I’ve come across a lot of really interesting, underrated, unique, or (as some might say) “un-pythonic” tricks to really level up what Python can do.

That’s why I decided to compile the top 14 of said features alongside examples and additional resources if you want to dive deeper into any of them.

1. Typing Overloads

@overload is a decorator from Python’s typing module that lets you define multiple signatures for the same function. Each overload tells the type checker exactly what types to expect when specific parameters are passed in.

For example, the code below dictates that only list[str] can be returned if mode=split, and only str can be returned if mode=upper. (The Literal type also forces mode to be either one of split or upper)

from typing import Literal, overload

@overload
def transform(data: str, mode: Literal["split"]) -> list[str]:
    ...

@overload
def transform(data: str, mode: Literal["upper"]) -> str:
    ...

def transform(data: str, mode: Literal["split", "upper"]) -> list[str] | str:
    if mode == "split":
        return data.split()
    else:
        return data.upper()

split_words = transform("hello world", "split")  # Return type is list[str]
split_words[0]  # Type checker is happy

upper_words = transform("hello world", "upper")  # Return type is str
upper_words.lower()  # Type checker is happy

upper_words.append("!")  # Cannot access attribute "append" for "str"

Overloads can do more than just change return type based on arguments! In another example, we use typing overloads to ensure that either one of id OR username are passed in, but never both.

@overload
def get_user(id: int = ..., username: None = None) -> User:
    ...

@overload
def get_user(id: None = None, username: str = ...) -> User:
    ...

def get_user(id: int | None = None, username: str | None = None) -> User:
    ...

get_user(id=1)  # Works!
get_user(username="John")  # Works!
get_user(id=1, username="John")  # No overloads for "get_user" match the provided arguments

✨ Quick bonus trick: As you probably saw, Python also has support for String Literals. These help assert that only specific string values can be passed to a parameter, giving you even more type safety. Think of them like a lightweight form of Enums!

def set_color(color: Literal["red", "blue", "green"]) -> None:
    ...

set_color("red")
set_color("blue")
set_color("green")
set_color("fuchsia")  # Argument of type "Literal['fuchsia']" cannot be assigned to parameter "color"

Additional Resources

2. Keyword-only and Positional-only Arguments

By default, both required parameters and optional parameters can be assigned with both positional and keyword syntax. However, what if you don’t want that to happen? Keyword-only and Positional-only args let you control that.

def foo(a, b, /, c, d, *, e, f):
	#         ^        ^
	# Ever seen these before?
	...

* (asterisk) marks keyword-only parameters. Arguments after * must be passed as keyword arguments.

#   KW+POS | KW ONLY
#       vv | vv
def foo(a, *, b):
    ...

# == ALLOWED ==
foo(a=1, b=2)  # All keyword
foo(1, b=2)  # Half positional, half keyword

# == NOT ALLOWED ==
foo(1, 2)  # Cannot use positional for keyword-only parameter
#      ^

/ (forward slash) marks positional-only parameters. Arguments before / must be passed positionally and cannot be used as keyword arguments.

# POS ONLY | KW POS
#       vv | vv
def bar(a, /, b):
    ...

# == ALLOWED ==
bar(1, 2)  # All positional
bar(1, b=2)  # Half positional, half keyword

# == NOT ALLOWED ==
bar(a=1, b=2)  # Cannot use keyword for positional-only parameter
#   ^

Keyword-only and Positional-only arguments are especially helpful for API developers to enforce how their arguments may be used and passed in.

Additional Resources

3. Future Annotations

A quick history lesson into Python’s typing:

Python’s typing system started off as a hack. Function annotation syntax was first introduced with PEP 3107 back in Python 3.0 as purely an extra way to decorate functions with no actual type-checking functionality.

Proper specifications for type annotations were later added in Python 3.5 through PEP 484, but they were designed to be evaluated at bound / definition time. This worked great for simple cases, but it increasingly caused headaches with one type of problem: forward references.

This meant that forward references (using a type before it gets defined) required falling back to string literals, making the code less elegant and more error-prone.

# This won't work
class Foo:
    def action(self) -> Foo:
        # The `-> Foo` return annotation is evaluated immediately during definition,
        # but the class `Foo` is not yet fully defined at that point,
        # causing a NameError during type checking.
        ...

# This is the workaround -> Using string types
class Bar:
    def action(self) -> "Bar":
        # Workaround with string literals, but ugly and error-prone
        ...

Introduced as a PEP (Python Enhancement Proposal), PEP 563: Postponed Evaluation of Annotations aimed to fix this by changing when type annotations were evaluated. Instead of evaluating annotations at definition time, PEP 563 “string-ifies” types behind the scenes and postpones evaluation until they’re actually needed, typically during static analysis. This allows for cleaner forward references without explicitly defining string literals and reduces the runtime overhead of type annotations.

from __future__ import annotations

class Foo:
    def bar(self) -> Foo:  # Works now!
        ...

So what was the problem?

For type checkers, this change is largely transparent. But because PEP 563 implements this by essentially treating all types as strings behind the scenes, anything that relies on accessing return types at runtime (i.e., ORMs, serialization libraries, validators, dependency injectors, etc.) will have compatibility issues with the new setup.

That’s why even after ten years after the initial proposal, modern Python (3.13 as of writing this) still relies on the same hacked-together type system introduced in Python 3.5.

# ===== Regular Python Typing =====
def foobar() -> int:
    return 1

ret_type = foobar.__annotations__.get("return")
ret_type
# Returns: <class 'int'>
new_int = ret_type()

# ===== With Postponed Evaluation =====
from __future__ import annotations

def foobar() -> int:
    return 1

ret_type = foobar.__annotations__.get("return")
ret_type
# "int" (str)
new_int = ret_type()  # TypeError: 'str' object is not callable

Recently, PEP 649 proposes a new method to handle Python function and class annotations through deferred, or “lazy,” evaluation. Instead of evaluating annotations at the time of function or class definition, as is traditionally done, this approach delays their computation until they are actually accessed.

This is achieved by compiling the annotation expressions into a separate function, stored in a special __annotate__ attribute. When the __annotations__ attribute is accessed for the first time, this function is invoked to compute and cache the annotations, making them readily available for subsequent accesses.

# Example code from the PEP 649 proposal

class function:
    # __annotations__ on a function object is already a
    # "data descriptor" in Python, we're just changing
    # what it does
    @property
    def __annotations__(self):
        return self.__annotate__()

# ...

def annotate_foo():
    return {'x': int, 'y': MyType, 'return': float}

def foo(x = 3, y = "abc"):
    ...

foo.__annotate__ = annotate_foo

class MyType:
   ...

foo_y_annotation = foo.__annotations__['y']

This deferred evaluation strategy addresses issues like forward references and circular dependencies, as annotations are only evaluated when needed. Moreover, it enhances performance by avoiding the immediate computation of annotations that might not be used, and maintains full semantic information, supporting introspection and runtime type-checking tools.

✨ Bonus Fact: Since Python 3.11, Python now supports a “Self” type (PEP 673) that allows for proper typing of methods that return instances of their own class, solving this particular example of self-referential return types.

from typing import Self

class Foo:
    def bar(self) -> Self:
        ...

Additional Resources

4. Generics

Did you know that Python has Generics? In fact, since Python 3.12, a newer, sleeker, and sexier syntax for Generics was introduced.

class KVStore[K: str | int, V]:
    def __init__(self) -> None:
        self.store: dict[K, V] = {}

    def get(self, key: K) -> V:
        return self.store[key]

    def set(self, key: K, value: V) -> None:
        self.store[key] = value

kv = KVStore[str, int]()
kv.set("one", 1)
kv.set("two", 2)
kv.set("three", 3)

Python 3.5 initially introduced Generics through the TypeVar syntax. However, PEP 695 for Python 3.12 revamped type annotations with native syntax for generics, type aliases, and more.

# OLD SYNTAX - Python 3.5 to 3.11
from typing import Generic, TypeVar

UnBounded = TypeVar("UnBounded")
Bounded = TypeVar("Bounded", bound=int)
Constrained = TypeVar("Constrained", int, float)

class Foo(Generic[UnBounded, Bounded, Constrained]):
    def __init__(self, x: UnBounded, y: Bounded, z: Constrained) -> None:
        self.x = x
        self.y = y
        self.z = z

# NEW SYNTAX - Python 3.12+
class Foo[UnBounded, Bounded: int, Constrained: int | float]:
    def __init__(self, x: UnBounded, y: Bounded, z: Constrained) -> None:
        self.x = x
        self.y = y
        self.z = z

This change also introduces an even more powerful version of variadic generics. Meaning you can have an arbitrary number of type parameters for complex data structures and operations.

class Tuple[*Ts]:
    def __init__(self, *args: *Ts) -> None:
        self.values = args

# Works with any number of types!
pair = Tuple[str, int]("hello", 42)
triple = Tuple[str, int, bool]("world", 100, True)

Finally, as part of the 3.12 typing changes, Python also introduced a new concise syntax for type aliases!

# OLD SYNTAX - Python 3.5 to 3.9
from typing import NewType
Vector = NewType("Vector", list[float])

# OLD-ish SYNTAX - Python 3.10 to 3.11
from typing import TypeAlias
Vector: TypeAlias = list[float]

# NEW SYNTAX - Python 3.12+
type Vector = list[float]

Additional Resources

5. Protocols

One of Python’s major features (and also major complaints) is its support for Duck Typing. There’s a saying that goes:

“If it walks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.”

However, that raises the question: How do you type duck typing?

class Duck:
    def quack(self): print('Quack!')

class Person:
    def quack(self): print("I'm quacking!")

class Dog:
    def bark(self): print('Woof!')

def run_quack(obj):
    obj.quack()

run_quack(Duck())  # Works!
run_quack(Person())  # Works!
run_quack(Dog())  # Fails with AttributeError

That’s where Protocols come in. Protocols (also known as Structural Subtyping) are typing classes in Python defining the structure or behavior that classes can follow without the use of interfaces or inheritance.

from typing import Protocol

class Quackable(Protocol):
    def quack(self) -> None:
        ...  # The ellipsis indicates this is just a method signature

class Duck:
    def quack(self): print('Quack!')

class Dog:
    def bark(self): print('Woof!')

def run_quack(obj: Quackable):
    obj.quack()

run_quack(Duck())  # Works!
run_quack(Dog())  # Fails during TYPE CHECKING (not runtime)

In essence, Protocols check what your object can do, not what it is. They simply state that as long as an object implements certain methods or behaviors, it qualifies, regardless of its actual type or inheritance.

✨ Additional quick tip: Add the @runtime_checkable decorator if you want isinstance() checks to work alongside your Protocols!

@runtime_checkable
class Drawable(Protocol):
    def draw(self) -> None:
        ...

Additional Resources

6. Context Managers

Context Managers are objects that define the methods: __enter__() and __exit__(). The __enter__() method runs when you enter the with block, and the __exit__() method runs when you leave it (even if an exception occurs).

Contextlib simplifies this process by wrapping all that boilerplate code in a single easy-to-use decorator.

# OLD SYNTAX - Traditional OOP-style context manager
class retry:
    def __enter__(self):
        print("Entering Context")

    def __exit__(self, exc_type, exc_val, exc_tb):
        print("Exiting Context")

# NEW SYNTAX - New contextlib-based context manager
import contextlib

@contextlib.contextmanager
def retry():
    print("Entering Context")
    yield
    print("Exiting Context")

To create your own, write a function with the @contextlib.contextmanager decorator. Add setup code before yield, cleanup code after it. Any variables on yield will be passed in as additional context. That’s it.

The yield statement instructs the context manager to pause your function and lets content within the with block run.

import contextlib

@contextlib.contextmanager
def context():
    # Setup code here
    setup()
    yield (...)  # Any variables you want to be passed to the with block
    # Teardown code here
    takedown()

Overall, this is a much more concise and readable way of creating and using context managers in Python.

Additional Resources

7. Structural Pattern Matching

Introduced in Python 3.10, Structural Pattern Matching gives Python developers a powerful alternative to traditional conditional logic. At its most basic, the syntax looks like this:

match value:
    case pattern1:
        # code if value matches pattern1
    case pattern2:
        # code if value matches pattern2
    case _:
        # wildcard case (default)

The real power comes with destructuring! Match patterns break down complex data structures and extract values in a single step.

# Destructuring and matching tuples
match point:
    case (0, 0):
        return "Origin"
    case (0, y):
        return f"Y-axis at {y}"
    case (x, 0):
        return f"X-axis at {x}"
    case (x, y):
        return f"Point at ({x}, {y})"

# Using OR pattern (|) to match multiple patterns
match day:
    case ("Monday"
          | "Tuesday"
          | "Wednesday"
          | "Thursday"
          | "Friday"):
        return "Weekday"
    case "Saturday" | "Sunday":
        return "Weekend"

# Guard clauses with inline 'if' statements
match temperature:
    case temp if temp < 0:
        return "Freezing"
    case temp if temp < 20:
        return "Cold"
    case temp if temp < 30:
        return "Warm"
    case _:
        return "Hot"

# Capture entire collections using asterisk (*)
match numbers:
    case [f]:
        return f"First: {f}"
    case [f, l]:
        return f"First: {f}, Last: {l}"
    case [f, *m, l]:
        return f"First: {f}, Middle: {m}, Last: {l}"
    case []:
        return "Empty list"

You can also combine match-case with other Python features like walrus operators to create even more powerful patterns.

# Check if a packet is valid or not
packet: list[int] = [0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07]

match packet:
    case [c1, c2, *data, footer] if (  # Deconstruct packet into header, data, and footer
        (checksum := c1 + c2) == sum(data) and  # Check that the checksum is correct
        len(data) == footer  # Check that the data length is correct
    ):
        print(f"Packet received: {data} (Checksum: {checksum})")
    case [c1, c2, *data]:  # Failure case where structure is correct but checksum is wrong
        print(f"Packet received: {data} (Checksum Failed)")
    case [_, *__]:  # Failure case where packet is too short
        print("Invalid packet length")
    case []:  # Failure case where packet is empty
        print("Empty packet")
    case _:  # Failure case where packet is invalid
        print("Invalid packet")

Additional Resources

8. Python Slots

Slots are a way to potentially speed up the creation and access of any Python class.

TLDR: They define a fixed set of attributes for classes, optimizing and speeding up accesses during runtime.

class Person:
    __slots__ = ('name', 'age')

    def __init__(self, name, age):
        self.name = name
        self.age = age

Under the hood, Python classes store instance attributes in an internal dictionary called __dict__, meaning a hash table lookup is required each time you want to access a value.

In contrast, __slots__ uses an array-like structure where attributes can be looked up in true O(1) time, bringing a minor overall speed bump to Python.

# Without __slots__
class FooBar:
    def __init__(self):
        self.a = 1
        self.b = 2
        self.c = 3

f = FooBar()
print(f.__dict__)  # {'a': 1, 'b': 2, 'c': 3}

# With __slots__
class FooBar:
    __slots__ = ('a', 'b', 'c')

    def __init__(self):
        self.a = 1
        self.b = 2
        self.c = 3

f = FooBar()
print(f.__dict__)  # AttributeError
print(f.__slots__)  # ('a', 'b', 'c')

There is still debate about whether __slots__ is worth using, as it complicates class definitions with very marginal or no performance benefits at all. However, it is a useful tool to have in your arsenal if you ever need it.

Additional Resources

9. Python Nitpicks

9.1 For-else statements

If you ever need to check if a for loop completes without a break, for-else statements are a great way to accomplish this without using a temporary variable.

# ===== Don't write this =====
found_server = False  # Keep track of whether we found a server
for server in servers:
    if server.check_availability():
        primary_server = server
        found_server = True  # Set the flag to True
        break
if not found_server:
    # Use the backup server if no server was found
    primary_server = backup_server

# Continue execution with whatever server we found
deploy_application(primary_server)

# ===== Write this instead =====
for server in servers:
    if server.check_availability():
        primary_server = server
        break
else:
    # Use the backup server if no server was found
    primary_server = backup_server

# Continue execution with whatever server we found
deploy_application(primary_server)

9.2 Walrus Operator

If you need to define and evaluate a variable all in one expression, the Walrus Operator (new in Python 3.8 with PEP 572) is a quick way to accomplish just that.

# ===== Don't write this =====
response = get_user_input()
if response:
    print('You pressed:', response)
else:
    print('You pressed nothing')

# ===== Write this instead =====
if response := get_user_input():
    print('You pressed:', response)
else:
    print('You pressed nothing')

9.3 Short Circuit Evaluation

Short-circuit Evaluation is a shortcut for getting the “next available” or “next truthy” value in a list of expressions. It turns out you can simply chain or statements!

# ===== Don't write this =====
username, full_name, first_name = get_user_info()

if username is not None:
    display_name = username
elif full_name is not None:
    display_name = full_name
elif first_name is not None:
    display_name = first_name
else:
    display_name = "Anonymous"

# ===== Write this instead =====
username, full_name, first_name = get_user_info()

display_name = username or full_name or first_name or "Anonymous"

9.4 Operator Chaining

Finally, Python lets you chain comparison operators together to shorten up integer range comparisons, making them more readable than the equivalent boolean expressions.

# ===== Don't write this =====
if 0 < x and x < 10:
    print("x is between 0 and 10")

# ===== Write this instead =====
if 0 < x < 10:  # Instead of if 0 < x and x < 10
    print("x is between 0 and 10")

Additional Resources

10. Advanced f-string String Formatting

Python’s f-strings are no secret by now. Introduced in Python 3.6 with PEP 498, they are a better, cleaner, faster, and safer method of interpolating variables, objects, and expressions into strings.

But did you know there is more to f-strings than just inserting variables? There exists a hidden formatting syntax called the Format Mini-Language that allows you to have much greater control over string formatting.

print(f"{' [ Run Status ] ':=^50}")
print(f"[{time:%H:%M:%S}] Training Run {run_id=} status: {progress:.1%}")
print(f"Summary: {total_samples:,} samples processed")
print(f"Accuracy: {accuracy:.4f} | Loss: {loss:#.3g}")
print(f"Memory: {memory / 1e9:+.2f} GB")

Output:

=================== [ Run Status ] ===================
[11:16:37] Training Run run_id=42 status: 87.4%
Summary: 12,345,678 samples processed
Accuracy: 0.9876 | Loss: 0.0123
Memory: +2.75 GB

You can do things like enable debug expressions, apply number formatting (similar to str.format), add string padding, format datetime objects, and more! All within f-string format specifiers.

Regular f-strings

Hello World!

Debug Expressions

print(f"{name=}, {age=}")

name='Claude', age=3

Number Formatting

print(f"Pi: {pi:.2f}")
print(f"Avogadro: {avogadro:.2e}")
print(f"Big Number: {big_num:,}")
print(f"Hex: {num:#0x}")
print(f"Number: {num:09}")

Pi: 3.14
Avogadro: 6.02e+23
Big Number: 1,000,000
Hex: 0x1a4
Number: 000000420

String Padding

print(f"Left: |{word:<10}|")
print(f"Right: |{word:>10}|")
print(f"Center: |{word:^10}|")
print(f"Center *: |{word:*^10}|")

Left: |Python    |
Right: |    Python|
Center: |  Python  |
Center *: |**Python**|

Date Formatting

print(f"Date: {now:%Y-%m-%d}")
print(f"Time: {now:%H:%M:%S}")

Date: 2025-03-10
Time: 14:30:59

Percentage Formatting

print(f"Progress: {progress:.1%}")

Progress: 75.0%

Additional Resources

11. Cache / lru_cache

You can use the built-in @cache decorator to dramatically speed up recursive functions and expensive calculations! (which superseded @lru_cache in Python 3.9!)

from functools import cache

@cache
def fib(n):
    return n if n < 2 else fib(n-1) + fib(n-2)

Since Python 3.2, @lru_cache was introduced as part of the functools module for quick & clean function memoization. Starting with Python 3.9, @cache was added for the same effect with less code. lru_cache still exists if you want explicit control of the cache size.

FIB_CACHE = {}

# With Manual Caching :(
def fib(n):
    if n in FIB_CACHE:
        return FIB_CACHE[n]
    if n <= 2:
        return 1
    FIB_CACHE[n] = fib(n - 1) + fib(n - 2)
    return FIB_CACHE[n]

from functools import lru_cache

# Same code with lru_cache :)
@lru_cache(maxsize=None)
def fib(n):
    return n if n < 2 else fib(n-1) + fib(n-2)

from functools import cache

# Same code with new Python 3.9's cache :D
@cache
def fib(n):
    return n if n < 2 else fib(n-1) + fib(n-2)

Additional Resources

12. Python Futures

Did you know that Python has native Promise-like concurrency control?

from concurrent.futures import Future

# Manually create a Future Object
future = Future()

# Set its result whenever you want
future.set_result("Hello from the future!")

# Get the result
print(future.result())  # "Hello from the future!"

Python’s concurrent.futures module gives you direct control over async operations, just like JS Promises. For example, they let you attach callbacks that run when the result is ready (just like JS’s .then()).

from concurrent.futures import Future

future = Future()

# Add callbacks BEFORE or AFTER completion!
future.add_done_callback(lambda f: print(f"Got: {f.result()}"))

future.set_result("Async result")
# Prints: "Got: Async result"

future.add_done_callback(lambda f: print(f"After: {f.result()}"))
# Prints: "After: Async result"

Python Futures also come with primitives to handle exceptions, set timeouts, or stop tasks completely.

from concurrent.futures import Future
import time, threading

# Create and manage a future manually
future = Future()

# Background task function
def background_task():
    time.sleep(2)
    future.set_result("Done!")

thread = threading.Thread(target=background_task)
thread.daemon = True
thread.start()

# Try all control operations
print(f"Cancelled: {future.cancel()}")  # Likely False if started

try:
    # Wait at most 0.5 seconds
    result = future.result(timeout=0.5)
except TimeoutError:
    print("Timed out!")

# Create failed future
err_future = Future()
err_future.set_exception(ValueError("Failed"))
print(f"Has error: {bool(err_future.exception())}")

Just like modern JS, the asyncio module has its own Future that works seamlessly with Python’s async/await syntax:

import asyncio

async def main():
    future = asyncio.Future()

    # Set result after delay
    asyncio.create_task(set_after_delay(future))

    # Await just like a JS Promise!
    result = await future
    print(result)  # "Worth the wait!"

async def set_after_delay(future):
    await asyncio.sleep(1)
    future.set_result("Worth the wait!")

asyncio.run(main())

Finally, for CPU or I/O bound tasks, Python’s ThreadPoolExecutor can automatically create and manage futures for you.

from concurrent.futures import ThreadPoolExecutor
import time

def slow_task():
    time.sleep(1)
    return "Done!"

with ThreadPoolExecutor() as executor:
    # Returns a Future immediately
    future = executor.submit(slow_task)

    # Do other work while waiting...
    print("Working...")

    # Get result when needed
    print(future.result())

Additional Resources

13. Proxy Properties

Did you know you can make class attributes act as BOTH methods AND properties?!? This isn’t a built-in feature of Python, but instead a demonstration of what you can do with clever use of Python’s dunder (magic) methods and descriptors.

from typing import Callable, Generic, TypeVar, ParamSpec, Self

P = ParamSpec("P")
R = TypeVar("R")
T = TypeVar("T")

class ProxyProperty(Generic[P, R]):
    func: Callable[P, R]
    instance: object

    def __init__(self, func: Callable[P, R]) -> None:
        self.func = func

    def __get__(self, instance: object, _=None) -> Self:
        self.instance = instance
        return self

    def __call__(self, *args: P.args, **kwargs: P.kwargs) -> R:
        return self.func(self.instance, *args, **kwargs)

    def __repr__(self) -> str:
        return self.func(self.instance)

def proxy_property(func: Callable[P, R]) -> ProxyProperty[P, R]:
    return ProxyProperty(func)

class Container:
    @proxy_property
    def value(self, val: int = 5) -> str:
        return f"The value is: {val}"

# Example usage
c = Container()
print(c.value)      # Returns: The value is: 5
print(c.value(7))   # Returns: The value is: 7

How does this work under the hood? It comes down to Python’s Descriptor Protocol:

The __get__ method transforms the ProxyProperty object into a descriptor.
When you access c.value, Python calls __get__ which returns self (the descriptor instance).
The __repr__ method handles property access (returning default values).
The __call__ method handles method calls with parameters.

This creates a dual-purpose attribute that can be both read directly AND called like a function!

The benefit of this class is that it allows you to create intuitive APIs where a property might need configuration, or properties that should have sensible defaults but still allow for customization.

Additional Resources

Finally, introducing one of Python’s most powerful yet mysterious features: Metaclasses

class MyMetaclass(type):
    def __new__(cls, name, bases, namespace):
        # Magic happens here
        return super().__new__(cls, name, bases, namespace)

class MyClass(metaclass=MyMetaclass):
    pass

obj = MyClass()

Classes in Python aren’t just blueprints for objects. They’re objects too! And every object needs a class that created it. So what creates class objects? Metaclasses.

By default, Python uses the type metaclass to create all classes. For example, these two are equivalent to each other:

# Create a MyClass object
class MyClass:
    ...
obj = MyClass()

# Also creates a MyClass object
obj2 = type("MyClass", (), {})

To break down what those arguments mean, here is an example that creates a class with an attribute x and a method say_hi, that also subclasses off object.

# type(
#     name,
#     bases,
#     attributes
# )
CustomClass = type(
    'CustomClass',
    (object,),
    {'x': 5, 'say_hi': lambda self: 'Hello!'}
)

obj = CustomClass()
print(obj.x)  # 5
print(obj.say_hi())  # Hello!

In essence, Metaclasses let you customize and modify these arguments during class creation. For example, here is a metaclass that doubles every integer attribute for a class:

class DoubleAttrMeta(type):
    def __new__(cls, name, bases, namespace):
        new_namespace = {}
        for key, val in namespace.items():
            if isinstance(val, int):
                val *= 2
            new_namespace[key] = val
        return super().__new__(cls, name, bases, new_namespace)

class MyClass(metaclass=DoubleAttrMeta):
    x = 5
    y = 10

print(MyClass.x)  # 10
print(MyClass.y)  # 20

Here is another example of a metaclass that registers every class created into a registry.

# ===== Metaclass Solution =====
class RegisterMeta(type):
    registry = []
    def __new__(mcs, name, bases, attrs):
        cls = super().__new__(mcs, name, bases, attrs)
        mcs.registry.append(cls)
        return cls

The problem is, decorators could achieve this same goal without the use of black magic (and it’s often cleaner too).

# ===== Decorator Solution =====
def register(cls):
    registry.append(cls)
    return cls

@register
class MyClass:
    pass

And that kind of brings to light the biggest problem with metaclasses:

Almost 100% of the time, you will never need to touch them.

In your day-to-day development, 99% of your code won’t ever hit a use case where metaclasses could be useful. And of that 1%, 95% of those cases could just be solved with regular decorators, dunder methods, or just plain inheritance.

That’s why there is that one famous Python quote that goes:

Metaclasses are deeper magic than 99% of users should ever worry about. If you wonder whether you need them, you don’t. - Tim Peters

But if you are that 1% which has a unique enough problem that only metaclasses can solve, they are a powerful tool that lets you tinker with the internals of the Python object system.

Additional Resources

Fin

And that’s it folks! 14 of some of the most interesting & underrated Python features that I’ve encountered in my Python career.

If you’ve made it this far, shoot me a quick message as to which ones you’ve seen before and which ones you haven’t! I’d love to hear from you.

Happy Python-ing, y’all 🐍!

Read the whole story

emrox

22 hours ago

Hamburg, Germany

View Transition API and its Integration in NextJS
Wednesday April 23^rd, 2025 at 4:09 AM

https://tiim.ch/blog

View Transition API and its Integration in NextJS

🇫🇷 This post is also available in french

The View Transition API allows native animation of page state changes, without depending on third-party libraries. Recently, Next.js has experimentally integrated this feature.

Although this approach is still in the testing phase and minimally documented, it paves the way for simplifying animations that were once considered complex.

Before discussing its use in Next.js, I will briefly introduce the API in its native version for those who may not yet be familiar with it. If you are already familiar with the API, you can directly skip to this section.

What is the View Transition API?

The View Transition API is a native browser feature that allows animating DOM state or navigation changes without resorting to a third-party library like Framer Motion or GSAP. It significantly simplifies the integration of transitions/visual animations when updating a page's content.

This feature is not supported by all browsers. Currently, it's only supported by Chrome-based browsers and the Safari browser.

startViewTransition

The core of this API lies in the method startViewTransition.

document.startViewTransition(() => updateTheDOMSomehow())

Calling this method, and passing it a callback function that updates the DOM, triggers a view transition cycle.

What does this mean? Essentially, when calling this method, the API captures the state of the page. Once the operation is complete (the page capture), your DOM update function is called and the API then again captures the state of the page, after your DOM mutation.

The API then builds a tree that looks like this:

::view-transition 
└─ ::view-transition-group(root)
   └─ ::view-transition-image-pair(root)
      ├─ ::view-transition-old(root)
      └─ ::view-transition-new(root)

As the name suggests, ::view-transition-old represents the capture of the old view and, as you may have guessed, ::view-transition-new represents the current capture of the view.

The old view is animated in fade out, while the new one appears in fade in (via the CSS property opacity). This is the default behaviour, but it can of course be customised (this is the whole point).

Customising transitions

To customise view transitions, we will use the pseudo selectors ::view-transition.... in CSS.

So, if I want to make a slightly more complex transition (than a fade in/out), I can target my view transition and apply a CSS animation of my choice.

For example, here, I respectively apply my animations pop-in and pop-out that I would have defined earlier in my style sheet.

::view-transition-old(root) {
  animation: pop-out 0.3s ease;
}

::view-transition-new(root) {
  animation: pop-in 0.3s ease;
}

Target a specific element

In the previous example, we used a view transition on the whole page (root), but it is possible to target a specific element.

To do this, we must first assign it a view transition name (view-transition-name).

.box {
  view-transition-name: box;
}

We can then target the view transition associated with this element with the corresponding pseudo elements:

::view-transition-old(box) {
	animation: skew-out 0.3s ease;
}

::view-transition-new(box) {
  animation: skew-in 0.3s ease;
}

You must assign a unique view-transition-name to each element for the capture to work. If you want to animate several elements in the same way, you can use the view-transition-class: myClass property. In this case, you will need to prefix your class name with a period to select it with the pseudo-element (e.g., view-transition-old(.myClass) or view-transition-new(.myClass)).

Two Types of Transitions

View transitions fall into two categories.

Transitions on the same document and those on multi-documents (page change transition). Both categories rely on the same principles, with the difference that for a multi-documents transition, there is no need to call the startViewTransition method to start the transition. The navigation between the documents is what triggers the transition.

We are now generally up to date on the state of the View Transition API (as of the writing of this article).

If you wish to delve deeper into the API, I recommend the MDN documentation (although a little light), the W3C specification, and the many articles from Chrome For Developers on the subject.

Activating the Magic of Transitions in Next.js

Recently, a feature was introduced to facilitate the integration of the View Transition API in Next.js projects. But beware, we are stepping into very little documented territory here.

This feature, introduced in a release a few months ago, is still marked as experimental. At the time of writing, the official documentation is quite minimal on the topic (here is the link if you want to take a look) and resources remain scarce.

It was precisely this lack of documentation that led me to dig a little bit deeper.

Digging around, I stumbled upon a demo shared by Delba Oliveira, a developer at Vercel. This made me want to delve deeper into the subject and experiment directly with this new API in a small test project on my end. Here's what I gleaned from it.

Spoiler: it's already promising.

To use this feature in NextJS, you need to enable the experimental flag viewTransition. And use a version ≥ v15.2.0.

next.config.js

module.exports = {
  // ...
  experimental: {
    viewTransition: true,
  },
}

The Component `unstable_viewTransition`

Currently, React exposes an unstable_viewTransition component (yes, the name sets the tone). It takes several properties:

name: Equivalent to the view-transition-name in CSS.
className: To assign a view-transition-class to the element.
exit / enter: To add a class (CSS) for the exit or entrance animation of the element. (On mounting or unmounting the component)
And other properties that I've yet to explore but are typed and documented in the types of React.

In practical terms, here's what it might look like in the code:

import { unstable_viewTransition as ViewTransition } from 'react'

export default function MyComponent() {
  return (
    <ViewTransition name="box">
      <div className="box">Hello</div>
    </ViewTransition>
  )
}

Even though the article here talks about integration in Next, it is crucial to note that this is fundamentally a feature of React introduced by this pull request. This is why we import the component unstable_ViewTransition from React.

A demonstration

And now... a little homegrown demo to show what it's like in action in a mini NextJS blog 👇

In this demo, we use the multi-document view transition, so it's the navigation that triggers the transitions. I gave the same name to the <ViewTransition> component used in the /blog page and the /blog/post/[slug] page. So, when navigating between the two pages, the transition is applied to animate the page change between these two elements.

Apart from a little blur effect on the images, this demo is purely accomplished with the React API, in default mode, as presented above, without any additional configuration. Therefore, it's relatively simple to implement.

And here is the source code used for this demo.

Limitations and Perspectives

The experimental integration of the View Transition API within Next.js opens up interesting prospects for developing smoother interfaces. In the future, we could imagine configurations of predefined transitions between pages, similar to NuxtJS.

However, as I have mentioned several times throughout this article, this is a feature that is not yet entirely production-ready. The API may change and will likely continue to evolve.

Bonus: Creative uses of the View Transition API

As a bonus, I've gathered some examples of sites that use the View Transition API creatively so you can see the possibilities it opens up.

Resources

Read the whole story

emrox

1 day ago

Hamburg, Germany

The Problem With Modern Engineering Isn't Speed. It's Chaos.
Wednesday April 23^rd, 2025 at 3:48 AM

Last year, our team spent a lot of time interviewing fellow Platform, DevOps, DevEx, CI/CD, and SRE engineers, as well as engineering leaders, in order to better understand their day-to-day challenges. We began this effort to see how Earthfiles, one of our products, could serve engineering teams at scale. But as we spoke to more and more people, we realized that platform engineering as an industry is on a collision course with something far more painful and visceral than just build speed.

It was the summer of 2024, and we needed to turn open-source success into commercial success for Earthfiles. Eleven thousand GitHub stars. How hard could it be to monetize that traction?

To make venture-scale money, we needed to go up-market and figure out what makes mid-size companies and enterprises tick and how our product might be able to help them. So we started interviewing platform and engineering leaders across the industry. DocuSign, Affirm, Roblox, Palo Alto Networks, Twilio, LinkedIn, Box, Morgan Stanley, BNY, and many more. We spoke to over 100 of these.

We started with a simple question:

We were hoping to get validation that developer productivity is a top concern and then be able to further narrow down how CI/CD speed would be able to unlock developer efficiency. But of all these interviews, only one mentioned build speed as a top issue, and it was largely biased by a recent production incident where they couldn’t get the fix out quickly enough due to a slow end-to-end CI/CD process.

In fact, the top issues they typically mentioned had nothing to do with productivity - not on the surface, anyway. It had to do more with how to best manage the engineering chaos that becomes inevitable at scale. You see, in the era of containers and microservices, there has been a general trend for companies to give more and more freedom to individual dev teams. It’s a container - if it slots in nicely in production, there’s less of a concern about what’s inside the container. ¹

The increased freedom results in an explosion of diversity at the dev infrastructure layer. Within any given company, you’ll find a mix of programming languages, CI technologies, build scripts, packaging constructs, in-house scripts, adapters - you name it. Every team’s setup is a unique snowflake. Even within the same programming language ecosystem, different teams will set up their dev process completely differently. Completely different build, test, packaging logic. Completely different runtime versions. Completely different eng culture. So on and so forth. This craziness is now the norm. ²

“Explosion of diversity”

This core problem of tech stack diversity is what we heard more commonly in our interviews. The interesting aspect of it is that different companies explained it differently to us, and different personas in the organizations were impacted by different consequences.

Platform teams complained about the constant firefighting required to support every app team’s unique needs. App teams on the other hand are focused on shipping features quickly - they complained about having to reinvent the wheel over and over again, about being slowed down by rigid deployment blockers, and about being given production readiness requirements very late in the process. Security teams complained about not having any visibility into the chaos. Engineering leadership complained about not being able to enforce high-quality engineering standards and not being able to understand the level of maturity of each app.

Everybody complained in their own way about the same fundamental core issue: extreme tech diversity is impossible to govern efficiently.

The goal isn’t total standardization

The other thing we heard loud and clear is that going back to the pre-microservice era of more standardized tech stacks isn’t a solution. Freedom is useful and necessary. It enables innovation. And hey, for many orgs, even if they suddenly thought that freedom is a bad thing, it would be impossible to go back and rewrite all the existing functionality to make the tech stack consistent. It’s just too much work.

We took it all in.

The industry is seemingly facing a catch-22. You can’t have strong innovation without freedom. You can’t have high-quality engineering and security without standardization.

We became obsessed with this problem: How do you preserve freedom, but still enforce the right standards at scale?

How organizations deal with this today

After speaking to over 100 engineering leaders, we identified a handful of common strategies for dealing with engineering chaos. Each has its strengths but also major weaknesses.

Approach	Issues
1. Common CI/CD Templates – Centralizing workflows via reusable templates works well for companies that adopted them early. But in mature orgs, adoption is rarely 100%, and maintaining consistency is a losing battle.	Rigid, difficult to retrofit, and often resented by app teams.
2. Manual Checklists – Reviews per PR or before launches. Cheap and flexible, but prone to human error and rubber-stamping.	Inefficient, inconsistent, and lacks ongoing visibility.
3. Scorecards (IDPs) – Great for accountability and high-level visibility. But they’re shallow, with limited CI/CD support and no shift-left feedback.	Issues are discovered too late, and enforcement is manual and inconsistent.
4. Individual Vendor Tools – Best for depth in specific areas like code scanning, testing, or licensing. But without unification, coverage remains inconsistent and fragmented.	Too many dashboards, poor integration, no centralized control plane.
5. DIY Solutions – Custom internal systems provide deep insights but are costly and hard to maintain.	Scalability issues, limited shift-left feedback, and incomplete enforcement.
6. Doing Nothing – Policies without enforcement. It’s compliance theater: the intention is there, the tools exist, but there’s no way to track or govern what’s actually happening across teams.	Inconsistent enforcement, lack of visibility, massive risk.

Each approach tackles part of the problem in some way but none solves it entirely.

What now?

The more we listened, the more we realized our mission had to grow beyond what we first imagined.

We started out Earthly with the goal of helping teams tame CI/CD complexity in today’s world of diverse tech stacks. One way to do that is to empower teams managing CI/CD (both platform and app teams) to be more effective in how they develop and run CI scripts. Consistent and fast CI scripts means that collaboration barriers are greatly reduced between these diverse ecosystems, and engineering teams as a whole are more productive. Certainly, that is the mission of Earthfiles.

But, another way to look at it is to step back and address the bigger problem. Enterprises are struggling to tame not just CI/CD complexity, but SDLC complexity as a whole, because it’s riddled with the same diversity, but also entangled with the difficulties of managing people at scale and giving every team the freedom to innovate with the right tools for the job, but to do so safely, within guardrails that aren’t slowing them down.

Earthly Lunar: Monitoring for the SDLC

After over a hundred interviews, one insight became impossible to ignore: a significant chunk of production incidents originate from issues that could have been caught earlier in the software development lifecycle. And yet, while we’ve built a whole industry around monitoring and securing production systems, we treat everything before production like the Wild West.

This is why today we’re announcing Earthly Lunar.

Lunar is a platform for monitoring engineering practices at scale. It’s like production monitoring, except it targets everything that happens before production. It gives Platform, DevEx, Security, QA, and Compliance teams real-time visibility into how applications are being developed, together with the power to gradually enforce specific practices — across every project, in every PR and in every deployment.

Lunar works by instrumenting your existing CI/CD pipelines (no YAML changes needed) and source code repositories to collect structured metadata about how code is built, tested, scanned, and deployed. This metadata is then continuously evaluated against policies that you define—policies that are flexible, testable, and expressive enough to reflect your real-world engineering standards.

Want to block deployments that would violate compliance rules, like using unapproved licenses or bypassing required security scans? Or fail a PR if it introduces stale dependencies or vulnerable CI plugins? Or ensure that security-sensitive services are collecting SBOMs, running code scans, and deploying frequently enough to avoid operational drift? Lunar makes all of that possible—without requiring a wholesale rewrite of every team’s CI pipeline, and without sacrificing developer velocity.

And crucially, Lunar is designed to work with the messy reality of modern engineering. It’s not a one-size-fits-all template, and it doesn’t require rewriting every CI pipeline. Its instrumentation is flexible and centralized—meaning platform teams stay in control, app teams stay autonomous, and standards actually get enforced.

Finally

Engineering at scale is messy. You’ve got hundreds of services, dozens of teams, and a sprawling ecosystem of tools—each doing one part of the job. But stitching that all together into a coherent, reliable, and compliant software delivery process? That’s the hard part. And that’s what Earthly Lunar is here to solve.

If this sounds like a problem you’re facing, we’d love to show you how Lunar works in practice.

👉 Visit the Lunar homepage

👉 Book a demo

Read the whole story

emrox

1 day ago

Hamburg, Germany

To Sleep, Perchance… by Doug Thursday April 24th, 2025 at 4:26 AM

Setup

Create a script file

Import the theme

Input and output

Writing a recursive function

An alternative with a for loop

Writing to a file

Comparison criteria

What’s Superface and why is this comparison neutral

HERE

Google Maps Platform

Azure Maps

OpenCage

LocationIQ

TomTom Maps API

Nominatim

Pricing comparison

Small usage (up to 30,000 requests / month)

Medium usage (100,000 requests/month or 3,333/day)

High usage (300,000 requests/month or 10,000/day)

Conclusion: What’s the best geocoding API deal?

Resources

Updates

Table of Contents

1. Typing Overloads

Additional Resources

2. Keyword-only and Positional-only Arguments

Additional Resources

3. Future Annotations

Additional Resources

4. Generics

Additional Resources

5. Protocols

Additional Resources

6. Context Managers

Additional Resources

7. Structural Pattern Matching

Additional Resources

8. Python Slots

Additional Resources

9. Python Nitpicks

9.1 For-else statements

9.2 Walrus Operator

9.3 Short Circuit Evaluation

9.4 Operator Chaining

Additional Resources

10. Advanced f-string String Formatting

Regular f-strings

Debug Expressions

Number Formatting

String Padding

Date Formatting

Percentage Formatting

Additional Resources

11. Cache / lru_cache

Additional Resources

12. Python Futures

Additional Resources

13. Proxy Properties

Additional Resources

Additional Resources

Fin

startViewTransition

Customising transitions

Target a specific element

Two Types of Transitions

The Component unstable_viewTransition

A demonstration

“Explosion of diversity”

The goal isn’t total standardization

How organizations deal with this today

What now?

Earthly Lunar: Monitoring for the SDLC

Finally

To Sleep, Perchance… by Doug
Thursday April 24^th, 2025 at 4:26 AM

An alternative with a `for` loop

The Component `unstable_viewTransition`