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scripts for managing free-form, plain-text collections of flashcards

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Octocat-spinner-32 COPYING

The Oboeta Hybrid Flashcard System

This collection of simple scripts helps users manage simple, plain-text collections of flashcards. It focuses on the essence of flashcard systems: scheduling. It also provides some very simple programs for displaying flashcards. A lot of the inspiration for this project comes from and

"Oboeta" is a Japanese verb in the simple past tense. It means "remembered" or "memorized".


The Problem

I love electronic flashcards. There are so many things to like about them:

  1. They're easy to create, modify, and destroy.
  2. It's especially easy to automatically generate hordes of cards from a few sentences if they're formatted properly.
  3. It's easy to apply changes across electronic flashcard decks.
  4. Computers can schedule reviews and track progress more quickly and accurately than humans.
  5. Electronic flashcards are easy to back up and transport.
  6. They occupy very little physical space. (Hence (5).)

But I also hate the most popular flashcard programs, such as Anki. They're complex, buggy, too restrictive, and tied to GUIs and storage formats that make my skin crawl. (OK, SQLite isn't too bad, but extracting data from it is still a pain in the ass.) I tried many programs and was never satisfied. All I wanted was something that operated on plain text and separated flashcards from their metadata.

Plain text is an awesome way to store flashcards and their metadata because:

  1. plain text is universal: it'll be around when your grandchildren's grandchildren become worm food;
  2. plain text can be easily edited via any text editor;
  3. plain text files aren't tied to a particular program or library; and
  4. all standard UNIX/POSIX tools can manipulate plain text files.

And then there's my love for paper flashcards. I admit that they're a pain to create and manage, but there are reasons to use them:

  1. You can format paper flashcards however you want. No supporting tools or complicated formatting algorithms are necessary: Just write what you want and be done with it.
  2. Sometimes paper flashcards are easier to carry around and faster to use than a smart phone. I have a little plastic pencil case that I bought for about $5 into which my B7-sized flashcards fit perfectly. All I have to do to access them is unzip the case and pull them out.
  3. For people learning new languages with difficult writing systems (such as East Asian languages), paper flashcards force them to practice writing. Typing doesn't help.
  4. Some people feel better when they use paper flashcards. I'm one of them. I don't understand why, but I get that mysteriously good feeling that a lot of people say they have when they use paper products rather than electronic devices (e.g., for reading).
  5. Paper flashcards grab attention. Smart phones and laptops don't do that because they're common and everyone around the user assumes she's playing games, sending messages, or surfing the web. For language learners, the best thing about grabbing people's attention with flashcards is that it creates opportunities to practice. Curious people start conversations, which lead to new sentences, which lead to new flashcards. It's a beautiful circle.

The Solution

I wrote Oboeta to combine electronic and paper flashcards into a hybrid system. The scripts are deliberately minimalistic so that you can format the flashcard data however you want. Although I wrote Oboeta to help me maintain a hybrid flashcard system, I could build a full-featured flashcard program on top of it. But I don't plan to. (^_^) However, it does provide a barely-functional console- and HTTP-based review system.

Oboeta provides two scheduling systems. The first is based on the Leitner system, which forms buckets of flashcards, each bucket of which contains an associated interval in days. The intervals determine how much time is added to a card's due date when you pass it. This simple system provides only two responses for each card: "pass" and "fail". Oboeta used to use this Leitner system exclusively: I have retained it because others might like it.

The second scheduling system is a slight variation of version 2 of the SuperMemo algorithm (SM-2). Each card has an associated easiness factor, an interval in days, and an interval number, all of which determine how much time should be added to the card when you review it. SM-2 provides more fine-grained responses than Leitner systems: Instead of the binary pass/fail responses, you have to choose an integer in [0,5], where 0 means complete memory blackout and 5 means "Piece of cake!" Your response determines the card's other parameters.

Here's how the overall system works: You maintain a collection of (paper) flashcards organized any way you like provided that each one has a unique identifier. (I use monotonically-increasing positive integers for mine.) On the electronic side, you maintain two plain UTF-8-encoded text files:

  1. a DSV file (the "deck") containing one flashcard per line, each beginning with the flashcard's unique identifier; and
  2. a DSV file (the "log") containing records of flashcard reviews.

Oboeta is agnostic about the deck's data: It only expects that the file is a DSV file and that the first field of each line is a unique identifier. You can format everything else however you want. This makes adding, editing, and reformatting flashcards a cinch: Just edit the deck file. You can use any text-manipulating program to do this.

On the other hand, the requirements for the log are more stringent:

  1. Each nonempty line must have exactly three fields: a flashcard's identifier, a timestamp, and either of the '+' and '-' characters if your reviews use the Leitner system or an integer in the range [0,5].
  2. The flashcard's identifier need not actually name a flashcard. (This makes deleting flashcards easy: Just remove them from the deck. You can remove their entries in the log, too, but you don't have to.)
  3. The timestamp can be formatted however you wish, but you must be consistent.
  4. If your reviews use the Leitner system, then the third field must be either a single '+' character or a single '-' character. '+' indicates that you successfully reviewed the associated flashcard on the date represented by the timestamp, whereas '-' indicates that you failed. On the other hand, if your reviews use SM-2, then the third field must be an integer in the range [0,5].

Oboeta uses the log to schedule flashcards for review. You ask Oboeta to dump a bunch of new or due cards to the screen, select the corresponding paper flashcards, and review them. When you're finished reviewing your cards, update the log accordingly. Alternatively, you can use the console- and HTTP-based review scripts to review the cards on your computer, which will automatically update the log.


I wrote most of the code in Python 3. (Die-hard Python 2 fans can cry me a river: Python 3 is the new standard. Welcome to the future.) It runs fine with CPython, the standard implementation.

The Scripts

All of these scripts only depend on the standard Python 3 libraries. They can be executed independently but are designed to be plugged together via UNIX pipes or temporary files.

  • oleitner -- process the deck and log files using the Leitner system and display flashcards that are due for review on standard output
  • osm2 -- like oleitner, but use SM-2 instead of the Leitner system
  • oboeta -- review flashcards from standard input, shuffling and displaying them one at a time on standard output, while reading commands (pass, fail, quit) from a file (usually a named pipe)
  • oboetatty -- display cards read from a file (usually a named pipe) one at a time on standard output get user input from standard input, and write the results (pass, fail, quit) to a file (usually a named pipe) (this program is suitable for text-only flashcards)
  • oboetahttp -- like oboetatty, but read cards from standard input instead and serve the cards as HTML5 over HTTP
  • ocloze -- generate cloze deletion flashcards from standard input


Open a terminal, navigate to the directory containing Oboeta's source code, and execute the script, passing the directory where you want to install executables as the first parameter. For example:

$ ./ /usr/bin

This will copy the scripts to the specified directory. You might have to change users (e.g., run sudo) depending on which installation directory you select.


oleitner is straightforward: Check out its help message via its -h option. osm2's input and output formatting are a little more complicated, but the command's invocation is simpler than oleitner's. Check out its help message via its -h option for details.

oboeta is designed to work with oboetatty and oboetahttp, though you could write other programs to interact with it. oboeta functions as a flashcard randomizer, chooser, and logger; oboetatty and oboetahttp focus on displaying the flashcards that oboeta chooses. oboetatty requires two named pipes: one for receiving cards from oboeta and one for sending commands to oboeta. On the other hand, oboetahttp requires only one named pipe, which it uses to send commands to oboeta: oboetahttp reads cards from standard input. (See the Honden repo for some examples of how to hook these scripts together.)

It gets a little more complicated, though. You have to break up the single-line cards that oboeta prints into two lines per card before feeding them to oboetatty or oboetahttp. (The first line contains the front side's fields and the second line contains the back side's fields.) sed and awk scripts can handle this job.

Let's check out some example pipelines. Suppose your deck uses the SM-2 algorithm and you want reviews to have at most 20 old cards and 10 new ones. If you want to review the cards on the console using fields two and three as the front and back, respectively, then this Bourne shell code will do it:

mkfifo -m 0700 cardpipe commandpipe
( osm2 -n 20 -e 10 deck.log <deck.txt | oboeta -2 $commandpipe deck.log | awk '{
  print $2
  print $3
  system("")  # to flush awk's stdout buffer
 }' >$cardpipe ) &
oboetatty -2 $cardpipe $commandpipe

The -2 flags enable SM-2 support in oboeta and oboetatty.

If you want to review cards via your favorite web browser, then do this instead:

mkfifo -m 0700 commandpipe
osm2 -n 20 -e 10 deck.log <deck.txt | oboeta -2 $commandpipe deck.log | awk '{
  print $2
  print $3
  system("")  # to flush awk's stdout buffer
 }' | oboetahttp -2 >$commandpipe

Of course, you can insert your own text processing pipelines between the oboeta scripts. That's the beauty of writing decoupled text-based programs. For example, I like to insert a script between osm2 and oboeta to transform custom Japanese furigana (rubi) annotations into HTML5 <ruby> tags.

See ocloze's help message (-h option) for information about how to use it.

Sample Framework Built on Oboeta

If you want an example of a framework built on top of Oboeta, see my Honden repo.


All of the files in this collection have been dedicated to the public domain via the Creative Commons CC0 Public Domain Dedication in the hope that they would be circulated widely and without restriction. I won't make any money from this code and I feel that it's more important that other people are free to use, modify, and distribute it as they please, with or without charge, even if I could make money from this. Simply put, I like contributing to a healthy public domain. See the file COPYING for a complete copy of the public domain dedication.


I wrote these scripts by myself primarily for myself, but I hope that others will find them useful.

-- Joodan Van (伴上段), 2012年11月04日

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