Default opt-out column handling for external dataset joins/merges. Use when merging external tables, files, or lookup datasets into a dataset and you must preserve all columns unless explicitly excluded. Triggers: join/merge steps, enrichment, ETL/ELT, lookup table integration, data integration work.
Preserve all columns by default when merging external datasets; only drop explicitly listed helper columns. Prefer opt-out over opt-in column lists to avoid accidental data loss.
exclude_cols for temporary/helper fields only, then drop.joined = left.join(right, on=keys, how="left", suffix="_r")
if isinstance(joined, pl.LazyFrame):
schema_names = joined.collect_schema().names()