Fix KeyError 'GEO_ID' when CensusAPI gets both group and variables

[jinskeep-morpc]

Problem

Passing both group and variables to CensusAPI raised the following in melt(), for ACS and decennial endpoints alike:

KeyError: "The following id_vars or value_vars are not present in the DataFrame: ['GEO_ID']"

CensusAPI(Endpoint('dec/dhc', 2020), group='P1', scope='region15', variables=['P1_001N'])

Root cause

_build_request() sets get=<variables> whenever variables are given, but _fetch() sent any request with a group to _fetch_group(). The API returns GEO_ID/NAME automatically only for the group(...) query form. _fetch_variables() is the path that adds them to get explicitly. With both arguments, a plain variable list went through the group path, so the response had no GEO_ID.

Args	get= sent	GEO_ID returned
group only	group(P1)	yes
variables only	GEO_ID,NAME,P1_001N	yes
both (before fix)	P1_001N	no

Fix

_fetch() uses _fetch_group() only when variables is None. self.group is unchanged, so checking variables against the group and the group-based concept/universe labels still work.

Changes

• morpc_census/api.py: dispatch condition in _fetch()
• tests/test_api.py: new TestFetchDispatch (3 tests); the group+variables test fails before the fix
• CHANGELOG.md, reference/dev_notes.md: entries
• pyproject.toml: adds enlighten to dependencies. This is unrelated to the fix and was already pending locally.

Testing

• Full test suite: 337 passed
• Live API: group+variables calls on dec/dhc 2020, dec/pl 2020 and acs/acs5 2023 all return long data with geoidfq/name

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