SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame
pandas can’t tell whether your assignment modifies the original DataFrame or a temporary copy.
Seen on:
Python
Meaning
Chained indexing like df[df.x > 0]["y"] = 1 may write to a copy and silently do nothing. Use .loc in a single step, or .copy() when you want an independent subset.
Common causes
- Chained indexing assignment
- Modifying a filtered subset later
⚡ Quick fix
- Use df.loc[df.x > 0, "y"] = 1
- Make subsets explicit: sub = df[df.x > 0].copy()
Detailed fix by platform
Python
df.loc[df["status"] == "new", "priority"] = "high"
How to diagnose
- Line — Which assignment?
- Intent — Modify original or a copy?
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Last updated 2 Oct 2026