Conceptually, roots is a set. Also searching it as a set is a tiny bit faster (#3338)
diff --git a/Lib/functools.py b/Lib/functools.py
index 0873f20..23ad160 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -193,7 +193,7 @@
def total_ordering(cls):
"""Class decorator that fills in missing ordering methods"""
# Find user-defined comparisons (not those inherited from object).
- roots = [op for op in _convert if getattr(cls, op, None) is not getattr(object, op, None)]
+ roots = {op for op in _convert if getattr(cls, op, None) is not getattr(object, op, None)}
if not roots:
raise ValueError('must define at least one ordering operation: < > <= >=')
root = max(roots) # prefer __lt__ to __le__ to __gt__ to __ge__