Anki SM-2

🌟 Anki's legacy SM-2-based spaced repetition algorithm 🌟

Python package implementing Anki's SM-2-based algorithm for spaced repetition scheduling.

Installation

You can install the anki-sm-2 python package from PyPI using pip:

pip install anki-sm-2

Quickstart

Import and initialize the Anki SM-2 Scheduler

from anki_sm_2 import Scheduler, Card, Rating

scheduler = Scheduler()

Create a new Card object

card = Card()

Choose a rating and review the card

# Rating.Again (==1) forgot the card
# Rating.Hard (==2) remembered the card with serious difficulty
# Rating.Good (==3) remembered the card after a hesitation
# Rating.Easy (==4) remembered the card easily

rating = Rating.Good

card, review_log = scheduler.review_card(card, rating)

print(f"Card rated {review_log.rating} at {review_log.review_datetime}")
# > Card rated 3 at 2024-10-31 01:36:57.080934+00:00

See when the card is due next

from datetime import datetime, timezone

due = card.due

# how much time between when the card is due and now
time_delta = due - datetime.now(timezone.utc)

print(f"Card due: at {due}")
print(f"Card due in {time_delta.seconds / 60} minutes")
# > Card due: at 2024-10-31 01:46:57.080934+00:00
# > Card due in 9.983333333333333 minutes

Usage

Timezone

Anki SM-2 uses UTC time only. You can still specify custom datetimes, but they must be UTC.

from anki_sm_2 import Scheduler, Card, Rating, ReviewLog
from datetime import datetime, timezone

scheduler = Scheduler()

# create a new card to be due on Jan. 1, 2024
card = Card(due=datetime(2024, 1, 1, 0, 0, 0, 0, timezone.utc)) # right
#card = Card(due=datetime(2024, 1, 1, 0, 0, 0, 0)) # wrong

# review the card on Jan. 2, 2024
card, review_log = scheduler.review_card(card=card, rating=Rating.Good, review_datetime=datetime(2024, 1, 2, 0, 0, 0, 0, timezone.utc)) # right
#card, review_log = scheduler.review_card(card=card, rating=Rating.Good, review_datetime=datetime(2024, 1, 2, 0, 0, 0, 0)) # wrong

Serialization

Scheduler, Card and ReviewLog objects are all json-serializable via their to_dict and from_dict methods for easy database storage:

# serialize before storage
scheduler_dict = scheduler.to_dict()
card_dict = card.to_dict()
review_log_dict = review_log.to_dict()

# deserialize from dict
scheduler = Scheduler.from_dict(scheduler_dict)
card = Card.from_dict(card_dict)
review_log = ReviewLog.from_dict(review_log_dict)

Versioning

This python package is currently unstable and adheres to the following versioning scheme:

• Minor version will increase when a backward-incompatible change is introduced.
• Patch version will increase when a bug is fixed, a new feature is added or when anything else backward compatible warrants a new release.

Once this package is considered stable, the Major version will be bumped to 1.0.0 and will follow semver.

Other SRS python packages

• FSRS
• SM-2
• Leitner System

Contribute

Checkout CONTRIBUTING to help improve Anki SM-2!

Official implementation

You can find the code for Anki's official Rust-based scheduler here.