Copy-on-Write and Performance in Python

From the Pandas cheat sheet · Plotting and Performance · verified Aug 2026

Copy-on-Write and Performance

Write predictable pandas 3 transformations.

python
df.loc[df["score"] < 0, "score"] = 0
📌 Copy-on-Write is the only mode in pandas 3
⚠️ Chained assignment cannot modify the original
⚡ Vectorized operations usually beat row-wise apply
🎯 Measure memory and runtime before optimizing
copy-on-writeperformancepandas-3

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