My Google Summer of Code 2022 summary

What and for whom

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Organization: MetaBrainz Foundation

Project: MusicBrainz Picard

Mentors: Laurent Monin (zas) & Philipp Wolfer (phw)

Main focus: Introducing single-instance mode in Picard 3.0

GSoC website: Link

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What has been done: TL;DR edition

• Picard works in single-instance mode by default, allowing to force-spawn a new instance
• Picard accepts not just file paths but also URLs, MBIDs and commands as command-line arguments
• The command-line arguments are sent to the existing instance (and processed by it) if possible
• Picard can execute commands passed by the command-line interface; e.g. save all files, show the Picard window or close the app
• Picard can also load the commands from a text file

List of PRs

Single instance mode:

• metabrainz/picard#2116: A big commit where the whole single-instance mode for Picard was designed and introduced (only for file paths though)
• metabrainz/picard#2135: Fixed problems with exiting the app, caused by metabrainz/picard#2116
• metabrainz/picard#2130: Supported URLs (with MBIDs) and mbid:// links (documented there) can be passed with file paths via CLI to an existing (or to a new one) instance
• metabrainz/picard#2137: Supported commands (like QUIT or SHOW) can be passed via CLI to an existing instance

Picard remote commands enhancements:

• metabrainz/picard#2141: REMOVE_EMPTY & REMOVE_UNCLUSTERED commands added
• metabrainz/picard#2142: LOAD command, extending the positional arguments' functionality, added
• metabrainz/picard#2143: FROM_FILE command, executing a command pipeline from a given file, added
• metabrainz/picard#2144: CLEAR_LOGS command added
• metabrainz/picard#2145: Fixed errors with the FROM_FILE command
• metabrainz/picard#2146: WRITE_LOGS command, allowing to save Picard logs into a file, added

Code refactoring:

• metabrainz/picard#2080: Code explicitly marked as deprecated got removed, my initial commit to get to know the Picard codebase and workflow
• metabrainz/picard#2127: Minor patch, unparsed args are now ignored as they were not used anywhere
• metabrainz/picard#2139: Refactored the whole process of passing arguments to Picard, replaced '%'-formatted strings with f-strings, more than one arguments can be passed correctly to a command

Other:

• metabrainz/picard#2122 + metabrainz/picard#2126: Github Actions gives quicker feedback by shortening the timeouts from 6 hours to 30 minutes
• metabrainz/picard-docs#174: Documented my changes

What I have learnt during GSoC 2022

• How to work with other people on GitHub
• How to improve my git experience (e.g. hooks)
• How one can handle inter-process communication, basically I have researched:
  • pipes
  • named pipes
  • sockets
  • dbus
• How to use Windows API with Python
• Differences between Windows and Unix pipes
• \0 is the only character that is prohibited on both Windows & Unix in path names
• /tmp is not the recommended way to store non-persistent app data on *nix
• os._exit might be useful when pythonic threads get broken
• Importing a tuple in Python is underrated. git diff gets cleaner, as one sees only the additions

Some personal thoughts

• Python is a really decent language that helps with starting one's programming journey but the deeper I went, the more annoyances I have encountered (that is why I ended up starting to work as a C++ dev)
• Ultra-safety is a double-edged sword: good luck terminating Pythonic futures/threads with file operations
• CI/CD and testing in general is as important as decent codebase
• If one can plan their time well, flexible work hours make their work both more effective and more enjoyable
• Python sometimes change for worse or breaks the code without any reason (e.g. they have switched from using a mode into w on pipes, ref: LINK)
• I will not start any new personal project in Python (especially one using multi-threading, multiple processes etc.), unless forced to do so. Nu for scripting, filling the niche & exploring the functional programming, some statically-typed languages for bigger projects, games, research, etc.
• Impostor syndrome is just an another excuse to procrastinate. Do not be scared to learn & do new things but also ask smart questions. Everyone makes mistakes but if you made it to this org, you are a good fit and have enough qualifications

Special thanks

The whole MetaBrainz community is awesome and I am glad I have become a part of it, but I would like to express my special gratitude to the people I have directly worked with in any way :) (alphabetical order by github username)

• atj
• phw
• rdswift: You were so helpful I consider you my 3rd mentor here.
• zas