openskill.py

6.2.0 verified Fri May 01 auth: no python

Multiplayer rating system implementing the Weng-Lin models (Plackett-Luce, Bradley-Terry, Thurstone-Mosteller). Pure Python, no dependencies. Version 6.2.0 requires Python ~=3.10. Active development with regular releases.

pip install openskill

Common errors

error ImportError: cannot import name 'rate' from 'openskill' ↓

cause Trying to import rate as a top-level function directly, but it's a module function.

fix

Use import openskill then openskill.rate(...).

error AttributeError: module 'openskill' has no attribute 'Rating' ↓

cause typo: 'Rating' not 'rating'.

fix

Use openskill.Rating() (capital R).

error ValueError: A team should have at least one player ↓

cause Passing an empty list as a team.

fix

Ensure each team has at least one Rating object.

error TypeError: __init__() got an unexpected keyword argument 'limit_sigma' ↓

cause Using a pre-6.0.0 version where limit_sigma wasn't a parameter.

fix

Upgrade to openskill>=6.0.0 or omit the parameter.

Warnings

breaking In v6.0.0, the `limit_sigma` parameter is no longer implicitly set; you must pass it explicitly if you want sigma to have a floor. ↓

fix Add `limit_sigma=True` to your rating or create Rating objects with `limit_sigma` parameter.

breaking v6.1.3 fixed a critical bug where players could gain infinite rating under certain conditions. Ensure you are on at least 6.1.3. ↓

fix Upgrade to openskill>=6.1.3.

deprecated Python 3.9 support dropped in v6.0.1. Use Python 3.10+. ↓

fix Use Python >=3.10.

gotcha The `rate` function expects a list of lists (teams) and returns updated teams. Mutating the input objects may lead to unexpected results. ↓

fix Treat tuples as immutable; do not modify original Rating objects after passing to rate.

gotcha Ranks are zero-indexed (lower rank = better). If you pass ranks incorrectly, win/loss direction may invert. ↓

fix Use ranks=[0,1] where team1 is better (lower rank) than team2.

Imports

openskill
wrong
```
from openskill import *
```
correct
```
import openskill
```
Wildcard imports are discouraged; import the module and use its functions.
rate
```
openskill.rate(t1, t2)
```

Quickstart

Simple example: two players, one match, team1 wins.

import openskill

# Define two teams with one player each
team1 = [openskill.Rating(mu=25, sigma=8.33)]
team2 = [openskill.Rating(mu=25, sigma=8.33)]

# Team1 wins (lower rank is better, ranks default to 0,1,...)
team1, team2 = openskill.rate([team1, team2], ranks=[0, 1])

print(team1[0])
print(team2[0])