[thomaspinder]

Summary

get_data named each column by its CBS title. When two columns share a title, the later one overwrote the earlier without any warning. 85592NED (consumer energy prices) has six titles that appear under both Aardgas and Elektriciteit, so all six gas columns came back holding electricity values. columns= had the same collision: columns=["Transporttarief"] quietly selected the electricity column.

 get_data(table)
-  column_map = {key: title}                      # shared titles collide
+  column_map = _column_names(props)
+    shared title -> "<topic group>: <title>"     # "Aardgas: Transporttarief"
+    still shared -> "<title> (<key>)"            # "Totaal (Totaal_1)"
   if columns:
+    a shared bare title raises ValueError listing the qualified names

Titles that aren't shared are unchanged, so existing column names stay the same. The getting-started docs now describe the rule.

Evidence

• Before: get_data("85592NED") returns 11 columns, and Transporttarief holds 394.11 €/yr, which is the electricity tariff.
  After: it returns 17 columns, with Aardgas: Transporttarief = 221.79 and Elektriciteit: Transporttarief = 394.11. Both match the raw OData values (Transporttarief_1, Transporttarief_7) for September 2026, excluding VAT.
• After: get_data("85592NED", columns=["Transporttarief"]) raises ValueError: 'Transporttarief' is the title of several columns in 85592NED; use one of ['Aardgas: Transporttarief', 'Elektriciteit: Transporttarief'].
• New tests in TestGetDataDuplicateTitles, all four failing on main and passing here:
  • test_shared_titles_are_qualified_by_group
  • test_shared_titles_without_group_fall_back_to_key
  • test_columns_accepts_qualified_title
  • test_columns_rejects_shared_title
• All 57 tests pass. ruff check, ruff format --check and ty check are clean.

Merge Danger

Door: two-way

Blast Radius: column names

• In tables with shared titles, column names change: Transporttarief becomes Aardgas: Transporttarief / Elektriciteit: Transporttarief. Code that indexed the bare name breaks with a ColumnNotFoundError. It was reading the wrong series before, so failing loudly is the intended outcome.
• columns= with a shared bare title now raises rather than picking one.
• An empty result no longer contains a stray column named after the last topic group. Topic groups have an empty key and are no longer treated as columns.

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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