glicko2

2.1.0 verified Sat May 09 auth: no python

A Python implementation of the Glicko-2 rating system, used for ranking players in games like chess or esports. Current version 2.1.0, requires Python >=3.7. Maintained, release cadence irregular.

pip install glicko2

Common errors

error AttributeError: module 'glicko2' has no attribute 'Player' ↓

cause Common mistake: importing the module instead of the class.

fix

Use 'from glicko2 import Player' instead of 'import glicko2'.

error TypeError: update_player() missing 1 required positional argument: 'scores' ↓

cause Calling update_player with only opponent list, missing scores list.

fix

Provide both opponent list and scores list, e.g., update_player([opponent], [1.0]) for a win.

error ValueError: The ratings list must contain at least 1 opponent ↓

cause Passing an empty list to update_player.

fix

Ensure opponents list is non-empty before calling update_player.

Warnings

gotcha The Player.update_player() method modifies the player in place; it does not return a new Player object. ↓

fix Call update_player and then access the updated attributes on the same object.

gotcha If you pass an empty list of opponents to update_player, the player's rating will drift toward the mean, which can cause unexpected rating changes. ↓

fix Only call update_player with non-empty opponent lists and corresponding scores.

deprecated The function glicko2.glicko2() is deprecated in favor of the Player class interface. Direct function usage may be removed in future versions. ↓

fix Use the Player class and its update_player method instead.

Imports

Player
wrong
```
import glicko2
```
correct
```
from glicko2 import Player
```
Direct import of module does not give attributes; use explicit class import.

Quickstart

Create two players, simulate a match, and print updated ratings.

from glicko2 import Player

# Initialize with default rating (1500), rating deviation (200), volatility (0.06)
p1 = Player()
p2 = Player()

# Simulate a match: p1 wins
p1.update_player([p2], [1.0])
p2.update_player([p1], [0.0])

print(p1.rating, p1.rd, p1.vol)
print(p2.rating, p2.rd, p2.vol)