Today I Learned (TIL)

TIL stands for today I learned. This is a collection of small, interesting things I’ve learnt, which I thought were worth remembering and sharing with other people.

If you want to follow along, these posts have their own RSS feed.

• The caret anchor (^) matches differently in Python and Ruby

• Collapsing whitespace in a Liquid template

  Output an empty string with stripped whitespace, that is {{- "" -}}.

• Python has a builtin tool to do rot13 (among other things)

  Look in the codecs module.

• The “MCP” in Archivematica stands for “Master Control Program”

  It’s nothing to do with generative AI.

• Get a list of values in a JSON object with jq

  The equivalent to Python’s dict.values() is jq '[.[]]'.

• The person who runs the Cambridge NTP servers has an excellent email address

• The @ symbol was added to Morse code in 2004

  It was added in May 2004, it’s the first new symbol since the Second World War, and the French have a cute name for it. The rest of Morse code has some surprising omissions.

• My preferred options for SmartyPants in Python

  smartypants.smartypants(…, Attr.default | Attr.u)

• Get the avatar URL for a Bluesky user

  Make a request to the app.bsky.actor.getProfile endpoint, passing their handle as the actor parameter.

• Looking up posts in the Bluesky API

  Install the atproto package, construct a client with your username/password, then call the get_post_thread method with your at:// URI.

• Using zipstream to stream new zip files to object storage with boto3

  You can construct a zipstream.ZipFile, add files, then wrap it in a file-like object to upload it with S3.upload_fileobj.

• Using Linode object storage and boto3

  If you’re calling put_object, you need the config option request_checksum_calculation = "when_required".

• Disable HTTP Basic Auth for certain pages in Caddy

  Define a matcher that negates the routes you want to be public, then use that with your basic_auth directive.

• Group nodes in a Mermaid flowchart by putting them in a subgraph

• Show a list of checkboxes in a WTForms form

  Subclass SelectMultipleField and override the widget and option_widget fields.

• Combine arrows in Mermaid by using an invisible node

• Redacting sensitive information from gunicorn access logs

  Create a subclass of gunicorn.glogging.Logger, and redact information in the atoms() method.

• Listen for the popstate event to see when the user clicks the “back” button

  More generally, it fires whenever the user is navigating the session history.

• Python’s f-strings support = for self-documenting expressions

  The f-string f"{x=}" expands to f"x={x}".

• The error “No aggregated item, sequence was empty” comes from Jinja2

  You get this error message if you try to use Jinja2’s filters to get the min/max of an empty sequence.

• Go’s compiler is smart enough to spot division by zero errors

• Print a comma-separated number in Python with {num:,}

  You can use {num:,} to insert a comma every three digits, {num:_} to insert an underscore every three digits, and {num:n} to insert a locale-aware digit separator.

• How do I find photos of a person on Flickr?

  https://www.flickr.com/people/{path_identifier}/photosof

• How does Flickr’s getLicenseHistory handle photos with no license changes?

• When fixing mojibake, use ftfy.fix_and_explain() to understand how it’s fixing a piece of text

• Why isn’t delete_where() deleting rows in sqlite-utils?

  The delete_where() function doesn’t auto-commit, so you need to wrap it with db.conn or something else to trigger the commit.

• console.log() holds a reference to an object, not a copy of it

  When you view an array/object with console.log(), you see the contents at the time you expand it, not as it existed when you called console.log().

• How to get a macOS file/folder icon in Swift

  Use NSWorkspace.shared.icon to get the icon as an NSImage, then you can save it to disk or do something else with it.

• Create an animated placeholder box with CSS

• What does Flickr return in the flickr.photo.getSizes API for videos?

  The video’s owner will get the URL to the original video file as “Video Original”, otherwise you should look for the largest video size.

• Getting and setting the cover image from an EPUB file

• How to find the content.opf in an EPUB file

• Restricting routes to pre-approved IP addresses in Caddy

• How to find the biggest files backed up by Backblaze

  Look at the file /Library/Backblaze.bzpkg/bzdata/bzfilelists/bigfilelist.dat.

• Editing a filename in Finder will convert it to NFD

  Even if the filename looks the same, it may be invisibly converted to a different sequence of bytes.

• Creating a reverse proxy to a multi-site server with Caddy

  You need to add Host headers and HTTPS configuration to your reverse_proxy block.

• How to get the target of an HTTP redirect with curl

• What is the author_name in the list of tags on a Flickr photo?

  When you call the flickr.photos.getInfo API, each tag is attributed to an author. The author_name is their username, not their realname.

• How to get a user’s email address with the Flickr API

  The flickr.profile.getProfile API returns somebody’s email address, but only if you’re allowed to see it.

• HTML strings may not be equivalent if you minify them

  There’s a lot of whitespace in HTML which looks irrelevant at first glance, but may be significant and cause the document to render differently.

• How do the ispublic, isfriend and isfamily flags work in the Flickr API?

• How to get the expiry date of an HTTPS certificate with Python

  Connect to the domain using the socket module, then use the getpeercert() method on the connection to get information about the HTTPS certificate.

• Create solid-colour image placeholders to show before an image loads

• Get an image from a video with ffmpeg

• Get the embedded artwork from an MP3 file

  Use the command eyeD3 [MP3_FILE] --write-images [FOLDER].

• Convert an animated GIF to an MP4 with ffmpeg

• Using the Wikimedia Commons API to tell if a file has been deleted

• How to get the selected item in Finder using AppleScript

• Removing letterboxing from a video screenshot with ImageMagick

  Using -trim will remove the black portions and leave you the unletterboxed image.

• How to highlight Python console sessions in Jekyll

  Adding a couple of options to the console lexer (console?lang=python&prompt=>>>) gets you syntax highlighting for a Python console session.

• Get a Palette colour as a command-line argument with Clap

  Wrapping a Palette:Srgb in a struct and implementing FromStr for the struct allows you to take hexadecimal colours as command-line inputs.

• How to get the filename/size without downloading a file in curl

  You can do some fun stuff with the --write-out flag and variables.

• How to count how many Discord messages were sent on a given day

  Using the During filter gives me a count of how many messages were being sent.

• How to see the HTTP requests being made by pywikibot

  To see exactly what HTTP requests were being made, I modified the library so that betamax would record requests.

• How to embed an inline SVG in a CSS rule

  Modern browsers allow you to embed the SVG almost as-is, with just a couple of characters that need escaping – no base64 required!

• How to shuffle an array in a Jekyll template

  If you want an array in random order, you can use the sample filter to get a random sample of the same size as the original array.

• Checking if a URL has changed when you fetch it over HTTP

  When you make an HTTP request, you can use the If-Modified-Since header to get a 304 Not Modified if nothing has changed since your last request.

• Why is Pillow rotating my image when I save it?

  Images can have orientation specified in their EXIF metadata, which isn’t preserved when you open and save an image with Pillow.

• How to change the name of an internal link in an Obsidian table

  Escaping the pipe like [[filename\|display text]] allows you to customise the of a link in a table.

• Getting a boto3 Session for an IAM role using Python

  Why I use Sessions in boto3, and the Python function I use to create them.

• How much will Mastodon instances try to re-send messages?

• Get my Netlify bandwidth usage from the API

• How to restrict a page to specific IP addresses

• How to parse URLs in JXA

• How to check when an HTTPS certificate expires

• What happens when you replace a photo on Flickr?

• Use the {% raw %} tag to describe Liquid in Liquid

  If you’re trying to write about using Liquid tags in a Liquid-based site, wrapping your tags in the {% raw %} tag will prevent them being rendered.

• What characters are allowed in titles on Wikimedia Commons?

• How to do offline geo-lookups of IP addresses

  MaxMind offer databases you can do to look up IP addresses without sending the address off to a remote service.

• How to move files when you need sudo on the remote server

• Use the {% capture %} tag to assign complex strings to variables

  If you want to get a string that’s semi-complicated to construct, you can put a “mini-template” in the {% capture %} tag to build it over multiple lines.

• WordPress URLs that get hammered by spammers

• Manage MP3 metadata from iTunes with eyed3

• How to create flag emojis for countries in Python

• Use the IMAGE function to insert an image into a spreadsheet

• Pausing the animation of <svg> elements can affect child <svg> elements differently in different browsers

• Running the Netlify CLI in GitHub Actions

• Get and manipulate the contents of a page in Safari with "do JavaScript"

• SVGs are only rendered on GitHub if you use an <img> that points to another file

• Animate an attribute of an element with <animate>

• How to delete albums

• Live Text is aware of how hyphenation works (kinda)

• Go between M-IDs and filenames on Wikimedia Commons

• Why I prefer XML to JSON in the Wikimedia Commons APIs

  The XML-to-JSON conversion leads to some inconsistent behaviour, especially in corner cases of the API.

• How to do resumable downloads with curl

• Find files that use a particular SDC field

• Why the term “snak” keeps appearing in the Wikidata API

• The acronym “woe” in the Flickr API stands for “Where On Earth”

• Use Unicode property escapes to detect emoji in JavaScript

• Finding the original page for a post on Mastodon

  Following the logged-out 302 Redirect takes you to the original post.

• How to use hex colours with the palette crate

  You can use Srgb::from_str() to parse a hexadecimal string as a colour in the palette crate.

• Calley-ope (calliope) Syndrome is pronouncing a word wrong because you’ve only ever read it on the page

• How do Dreamwidth posts IDs work?

  They were deliberately non-sequential as an anti-spam technique. It’s no longer required, but it’s in the codebase now and hasn’t been changed since it was written.

• DynamoDB: Conditional updates on nested fields

• Using TransportAPI and geopy to get the distance between stations

• The Content-Disposition header can be used to name a downloaded file

• How to set the clock on a Horstmann Electronic 7 water heater

• Why does Hypothesis try the same example three times before failing?

• How to set the clock on a Tricity Bendix SIE454 electric cooker

• How to set the clock on a Worcester 28CDi boiler

• Get an RSS feed of external audio posts on Tumblr

  If you add /podcast to a Tumblr site, you get a podcast-like RSS feed for all the external audio posts on that site.