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.

This exercise is part of the course

Scaling and Optimizing Data Pipelines with Polars

View Course

Exercise instructions

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

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

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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