Here is a spaced repetition algorithm that is well documented and easy to understand.
Features
- Introduces sub-decks for efficiently learning large decks (Super
useful!)
- Intuitive variable names and algorithm parameters. Fully
open-source with human-readable examples.
- Easily configurable
parameters to accommodate for different users' memorization
abilities.
- Computationally cheap to compute next card. No need to
run a computation on every card in the deck.
https://github.com/Jakobovski/SaneMemo.
Disclaimer: I am the author of SaneMemo.
import random
import datetime
# The number of times needed for the user to get the card correct(EASY) consecutively before removing the card from
# the current sub_deck.
CONSECUTIVE_CORRECT_TO_REMOVE_FROM_SUBDECK_WHEN_KNOWN = 2
CONSECUTIVE_CORRECT_TO_REMOVE_FROM_SUBDECK_WHEN_WILL_FORGET = 3
# The number of cards in the sub-deck
SUBDECK_SIZE = 15
REMINDER_RATE = 1.6
class Deck(object):
def __init__(self):
self.cards = []
# Used to make sure we don't display the same card twice
self.last_card = None
def add_card(self, card):
self.cards.append(card)
def get_next_card(self):
self.cards = sorted(self.cards) # Sorted by next_practice_time
sub_deck = self.cards[0:min(SUBDECK_SIZE, len(self.cards))]
card = random.choice(sub_deck)
# In case card == last card lets select again. We don't want to show the same card two times in a row.
while card == self.last_card:
card = random.choice(sub_deck)
self.last_card = card
return card
class Card(object):
def __init__(self, front, back):
self.front = front
self.back = back
self.next_practice_time = datetime.utc.now()
self.consecutive_correct_answer = 0
self.last_time_easy = datetime.utc.now()
def update(self, performance_str):
""" Updates the card after the user has seen it and answered how difficult it was. The user can provide one of
three options: [I_KNOW, KNOW_BUT_WILL_FORGET, DONT_KNOW].
"""
if performance_str == "KNOW_IT":
self.consecutive_correct_answer += 1
if self.consecutive_correct_answer >= CONSECUTIVE_CORRECT_TO_REMOVE_FROM_SUBDECK_WHEN_KNOWN:
days_since_last_easy = (datetime.utc.now() - self.last_time_easy).days
days_to_next_review = (days_since_last_easy + 2) * REMINDER_RATE
self.next_practice_time = datetime.utc.now() + datetime.time(days=days_to_next_review)
self.last_time_easy = datetime.utc.now()
else:
self.next_practice_time = datetime.utc.now()
elif performance_str == "KNOW_BUT_WILL_FORGET":
self.consecutive_correct_answer += 1
if self.consecutive_correct_answer >= CONSECUTIVE_CORRECT_TO_REMOVE_FROM_SUBDECK_WHEN_WILL_FORGET:
self.next_practice_time = datetime.utc.now() + datetime.time(days=1)
else:
self.next_practice_time = datetime.utc.now()
elif performance_str == "DONT_KNOW":
self.consecutive_correct_answer = 0
self.next_practice_time = datetime.utc.now()
def __cmp__(self, other):
"""Comparator or sorting cards by next_practice_time"""
if hasattr(other, 'next_practice_time'):
return self.number.__cmp__(other.next_practice_time)
