Overriding the inferred schema

When Polars scans the vendor export, it uses the first few rows to infer column types. The branch_code column uses 3-digit identifiers with leading zeros ("001", "002", …), but Polars sees integers and parses them as Int64, silently dropping the zeros. Override the schema so branch_code stays a string.

The inferred schema is already printed for you, so you can see what Polars guessed without any overrides.

Deze oefening maakt deel uit van de cursus

Scaling and Optimizing Data Pipelines with Polars

Bekijk cursus

Oefeninstructies

Override branch_code so it's read as pl.String.

Interactieve oefening met praktijkervaring

Probeer deze oefening door deze voorbeeldcode aan te vullen.

schema = pl.scan_csv(
    MESSY_CSV_PATH,
    separator=";",
    skip_rows=2,
    infer_schema_length=5,
    # Force branch_code to String
    schema_overrides={"____": pl.____},
).collect_schema()

print("\nOverridden schema:")
print(schema)

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