srsdb 0.9.0

SQLite database for tracking SRS learning state with FSRS and Ebisu algorithms

srsdb

A Python library for managing Spaced Repetition System (SRS) learning data using SQLite. Track the state of individual learning items with sophisticated scheduling algorithms.

Features

• 🧠 Multiple SRS Algorithms: FSRS (deterministic) and Ebisu (Bayesian)
• 💾 SQLite Backend: Persistent storage with flexible schema
• 📊 Detailed Tracking: Monitor difficulty, stability, review history, and more
• 🔄 Flexible Correctness: Rate answers on a 0-100 scale
• 🧪 Well Tested: Comprehensive test suite with 35+ unit tests
• 🐍 Python 3.8+: Compatible with modern Python versions
• 🔌 Optional Dependencies: Use FsrsDatabase without any dependencies, add Ebisu when needed

Installation

pip install -e .

Or for development:

pip install -e ".[dev]"

Example Databases

Explore pre-built example databases in the example/ directory:

• example/fsrs.db - Spanish vocabulary learning with FSRS (10 cards, 25 reviews)
• example/ebisu.db - Python programming concepts with Ebisu (10 cards, 44 reviews)

# View statistics
python example/view_stats.py

# Regenerate examples
python example/generate_examples.py

# Explore with SQLite
sqlite3 example/fsrs.db "SELECT * FROM fsrs_cards;"

See example/README.md for more details.

Quick Start

from datetime import datetime
from fsrs_database import FsrsDatabase

# Create a database instance
db = FsrsDatabase("my_learning.db")

# Record answering a question
now = datetime.now()
db.answer(now, "question_id_1", correctness=85)  # 85% correct

# Get cards that are due for review
due_cards = db.next(now)
print(f"Cards to review: {due_cards}")

# Check when the next review is scheduled
next_review = db.next_due_date()
print(f"Next review: {next_review}")

Interface: SrsDatabase

The SrsDatabase abstract base class defines the interface for all SRS implementations:

Constructor

SrsDatabase(database_file: str)

Initializes the database with a file path. The file is created if it doesn't exist.

Methods

answer(now: datetime, question_key: str, correct: int) -> None

Records the result of answering a question.

Parameters:

• now: The time the question was answered (doesn't have to be real-time, useful for testing)
• question_key: Unique identifier for the question
• correct: Correctness value from 0-100
  • 0 = completely wrong
  • 100 = completely correct
  • Values in between = degrees of correctness

The correctness value is internally converted to an appropriate value for the underlying SRS algorithm.

next(now: datetime) -> List[str]

Returns questions that are due for review as of the given time.

Parameters:

• now: The current time to check against

Returns:

• List of question keys in chronological order of due date

next_due_date() -> Optional[datetime]

Returns the date/time when the next question becomes due.

Returns:

• The next due date, or None if no questions are scheduled

Implementation: FsrsDatabase

The FsrsDatabase class implements the SrsDatabase interface using the FSRS algorithm, which tracks:

• Difficulty: How hard the card is (0-10 scale)
• Stability: Memory stability in days
• State: Card state (new, learning, review, relearning)
• Review History: Complete history of all reviews
• Lapses: Number of times the card was forgotten

Example Usage

from datetime import datetime, timedelta
from fsrs_database import FsrsDatabase

# Initialize database
db = FsrsDatabase("flashcards.db")

# Day 1: Learn new cards
day1 = datetime(2024, 1, 1, 10, 0, 0)

db.answer(day1, "spanish_hello", 90)      # Got it right!
db.answer(day1, "spanish_goodbye", 60)    # Mostly correct
db.answer(day1, "spanish_please", 20)     # Need more practice

# Day 2: Review due cards
day2 = day1 + timedelta(days=1)
due = db.next(day2)
print(f"Cards due: {due}")  # ['spanish_please']

for card in due:
    # Review the card and record the result
    db.answer(day2, card, 75)

# Day 7: Check what needs review
day7 = day1 + timedelta(days=7)
due = db.next(day7)
print(f"Cards due after a week: {due}")

# Check next scheduled review
next_review = db.next_due_date()
print(f"Next review scheduled: {next_review}")

Advanced Example: Learning Session

from datetime import datetime, timedelta
from fsrs_database import FsrsDatabase

def study_session(db, current_time, responses):
    """Simulate a study session with multiple card reviews."""

    # Get cards due for review
    due_cards = db.next(current_time)
    print(f"\n📚 Study session at {current_time}")
    print(f"Cards to review: {len(due_cards)}")

    # Review each card
    for card_id in due_cards:
        correctness = responses.get(card_id, 50)
        db.answer(current_time, card_id, correctness)

        emoji = "✅" if correctness >= 70 else "⚠️" if correctness >= 40 else "❌"
        print(f"  {emoji} {card_id}: {correctness}% correct")

    # Show next review time
    next_due = db.next_due_date()
    if next_due:
        days_until = (next_due - current_time).days
        print(f"📅 Next review in {days_until} day(s)")

# Initialize
db = FsrsDatabase("study.db")
start = datetime(2024, 1, 1, 9, 0, 0)

# Day 1: Initial learning
study_session(db, start, {
    "capitals_france": 100,
    "capitals_germany": 85,
    "capitals_italy": 60,
    "capitals_spain": 40,
})

# Day 3: First review
study_session(db, start + timedelta(days=3), {
    "capitals_spain": 80,
    "capitals_italy": 90,
})

# Day 10: Follow-up review
study_session(db, start + timedelta(days=10), {
    "capitals_france": 95,
    "capitals_germany": 100,
    "capitals_italy": 85,
    "capitals_spain": 70,
})

Implementation: EbisuDatabase

The EbisuDatabase class implements the SrsDatabase interface using the Ebisu Bayesian algorithm, which tracks:

• Alpha & Beta: Parameters of the Beta distribution on recall probability
• Half-life (t): Expected time until recall probability reaches 0.5
• Bayesian Updates: Uses quiz results to update beliefs about memory strength
• Review History: Complete history with recall probabilities

Note: Requires the ebisu package: pip install ebisu

Example Usage

from datetime import datetime, timedelta
from ebisu_database import EbisuDatabase

# Initialize database (requires ebisu package)
db = EbisuDatabase("learning.db")

# Day 1: Learn new vocabulary
day1 = datetime(2024, 1, 1, 9, 0, 0)

db.answer(day1, "vocab_apple", 95)       # Nearly perfect
db.answer(day1, "vocab_banana", 70)      # Pretty good
db.answer(day1, "vocab_cherry", 40)      # Struggling

# Day 3: Review cards that are due
day3 = day1 + timedelta(days=3)
due = db.next(day3)
print(f"Cards needing review: {due}")

# Cards are ordered by recall probability (lowest first)
for card in due:
    db.answer(day3, card, 80)  # Review with 80% correctness

# Check when next review is needed
next_review = db.next_due_date()
print(f"Next review: {next_review}")

Key Differences from FSRS

• Bayesian: Uses probabilistic modeling vs deterministic scheduling
• Adaptive: Continuously updates beliefs about memory strength
• Flexible: Supports soft-binary quiz results (0.0-1.0 success values)
• Half-life Based: Schedules reviews based on predicted forgetting curve

Database Schema

FsrsDatabase Tables

The FsrsDatabase creates two tables:

fsrs_cards

Stores the current state of each card:

• question_key (PRIMARY KEY): Unique card identifier
• difficulty: Card difficulty (0-10)
• stability: Memory stability in days
• state: Card state (0=new, 1=learning, 2=review, 3=relearning)
• due_date: When the card is next due
• reps: Total number of reviews
• lapses: Number of times forgotten

fsrs_reviews

Historical record of all reviews:

• id (PRIMARY KEY): Auto-incrementing review ID
• question_key: Card being reviewed
• review_time: When the review occurred
• rating: FSRS rating (1-4)
• state: Card state after review

EbisuDatabase Tables

The EbisuDatabase creates two tables:

ebisu_cards

Stores the current Bayesian model for each card:

• question_key (PRIMARY KEY): Unique card identifier
• alpha: Alpha parameter of Beta distribution
• beta: Beta parameter of Beta distribution
• t: Half-life in hours
• last_review: Timestamp of last review
• total_reviews: Total number of reviews

ebisu_reviews

Historical record of all reviews:

• id (PRIMARY KEY): Auto-incrementing review ID
• question_key: Card being reviewed
• review_time: When the review occurred
• correctness: Correctness value (0-100)
• recall_probability: Predicted recall before this review

Testing

Run the test suite:

# Using unittest
python -m unittest discover -v

# Using pytest (if installed)
pytest -v

Implementation Status

• ✅ SrsDatabase Interface: Complete
• ✅ FsrsDatabase: Fully implemented with comprehensive tests (17+ tests)
• ✅ EbisuDatabase: Fully implemented with comprehensive tests (18+ tests)

Future Enhancements

• Export/import functionality
• Statistics and analytics
• Card tagging and filtering
• Multiple deck support

Contributing

Contributions are welcome! Please ensure:

• All tests pass (python -m unittest discover)
• Code follows Python best practices
• New features include tests

License

MIT License - See LICENSE file for details

See Also

• FSRS Algorithm - Free Spaced Repetition Scheduler
• Ebisu Algorithm - Bayesian spaced repetition algorithm
• Ebisu on PyPI - Python implementation of Ebisu
• SuperMemo - Pioneer of spaced repetition
• Anki - Popular SRS flashcard application