[ENH] Add polars Engine Support to pd.read_csv()

[abujabarmubarak]

🚀 Pull Request: [ENH] Add polars Engine Support to pd.read_csv()

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❓ Problem Statement

Pandas' read_csv() function supports multiple engines like "c", "python", and "pyarrow" for reading CSV files. However, there is no built-in support for the high-performance Polars engine, which is known for its speed and efficiency in parsing large datasets.

✅ Community Request: Feature proposed in Issue #61813

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🛠️ Solution & What’s Included

This PR implements optional support for engine="polars" in pandas.read_csv() by:

1. Modifying readers.py:

   • Checks if engine is "polars".
   • Dynamically imports Polars and uses pl.read_csv(...).to_pandas() to return a pandas DataFrame.

   if kwds.get("engine") == "polars":
       try:
           import polars as pl  # type: ignore[import-untyped]
       except ImportError:
           raise ImportError("Polars is not installed. Please install it with 'pip install polars'.")
       df = pl.read_csv(filepath_or_buffer, **kwds).to_pandas()
       return df

2. Ensuring compatibility in engine validation:

   if engine not in ("c", "python", "pyarrow", "polars"):
       raise ValueError(f"Unknown engine: {engine}")

3. Version Updates:

   • Updated version to 2.3.3.dev0 in:
     • __init__.py
     • pyproject.toml

4. Testing:

   • Added a dedicated test: pandas/tests/io/parser/test_read_csv_polars.py

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💡 Example Usage

import pandas as pd

df = pd.read_csv("sample.csv", engine="polars")
print(df)

Input file: sample.csv

a,b
1,2
3,4

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🎯 Expected Output

   a  b
0  1  2
1  3  4

• The file is parsed using Polars under the hood and returned as a pandas.DataFrame.
• Performance benefits without changing the Pandas API.
• Optional: only active if polars is installed.

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📂 Files Modified

• pandas/io/parsers/readers.py → Add polars engine logic
• pandas/__init__.py → Version bump to 2.3.3.dev0
• pyproject.toml → Version update
• pandas/tests/io/parser/test_read_csv_polars.py → New test file added

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🧪 Tests

Test name: test_read_csv_with_polars

def test_read_csv_with_polars(tmp_path):
    pl = pytest.importorskip("polars")
    pd = pytest.importorskip("pandas")

    file = tmp_path / "sample.csv"
    file.write_text("a,b\n1,2\n3,4")

    df = pd.read_csv(file, engine="polars")

    assert df.equals(pd.DataFrame({"a": [1, 3], "b": [2, 4]}))

✅ Result: Passed with warning (unrelated deprecation from pyarrow)

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🧷 Notes

• Falls back to error if Polars is not installed.
• This is a non-breaking enhancement and does not affect existing functionality.
• Future expansion possible to support write or more Polars features.

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🔁 Feedback welcome!