Pandas

Pandas is the Excel of Python. v3.0 (2025/2026) enforces Copy-on-Write (CoW), finally fixing the SettingWithCopyWarning confusion.

When to Use

• Data Cleaning: Loading CSV/Excel/SQL and cleaning it.
• Time Series: Unmatched datetime indexing capabilities.
• Small/Medium Data: Features that fit in RAM.

Core Concepts

DataFrame / Series

2D tables and 1D arrays.

Copy-on-Write (CoW)

Views are always views, copies are always copies. Modifying a view triggers a copy only if necessary.

PyArrow Backend

Using Arrow memory format for speed and string handling (dtype="string[pyarrow]").

Best Practices (2025)

Do:

• Use PyArrow Strings: pd.options.future.infer_string = True (Default in 3.0).
• Use .query(): For cleaner filtering syntax.
• Migrate to CoW: Ensure your code doesn't rely on side-effects of views.

Don't:

• Don't iterate rows: Use vectorization (df['a'] + df['b']).

References

• Pandas Documentation