snakemake#4056)

Closes snakemake#4048 

### Problem
The `lookup()` function's `default` parameter was ignored when using
`query` with a pandas DataFrame. If a query returned no matching rows,
it returned an empty list `[]` instead of the provided default value.
The `default` parameter only worked with `dpath` (dictionary lookups).

  ### Solution
Added a check in the `do_query` function in `lookup.py` to return the
`default` value when the query result is empty and a default is
provided.

  ### Changes
- `src/snakemake/ioutils/lookup.py` — Added 2 lines to check for empty
query results and return the default value
- `tests/test_ioutils/Snakefile` — Added an assert to test that the
default value is returned for empty DataFrame queries
- `docs/snakefiles/rules.rst` — Updated documentation to reflect that
the `default` argument now works for both `dpath` and `query`

### QC
* [x] The changes are already covered by an existing test case
test_ioutils. Added a new assert in `tests/test_ioutils/Snakefile` to
test DataFrame default value behaviour.
* [x] The documentation (docs/) is updated: Updated
docs/snakefiles/rules.rst to remove the note that `default` is ignored
for queries.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Lookup function now returns the provided default value when queries
yield no results.
  * None is now a valid default value.

* **Documentation**
  * Updated lookup function behavior documentation.

* **Tests**
  * Added test coverage for lookup function with default value fallback.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

🤖 I have created a release *beep* *boop*
---


##
[9.17.0](v9.16.3...v9.17.0)
(2026-03-13)


### Features

* Allow storing snakemake metadata in files or databases
([#4012](#4012))
([dd75f31](dd75f31))
* Allow to specify comparison command per-unit test
([#3956](#3956))
([b88171c](b88171c))
* job table orderd topological when run is started
([#4018](#4018))
([75cf506](75cf506))
* lambda functions for priority in rules
([#3253](#3253))
([d2aa226](d2aa226))
* Make on... directive of modules accessible
([#4050](#4050))
([e9f2e1c](e9f2e1c))


### Bug Fixes

* adjust conda tests to not fail on apple silicon; fix
[#4040](#4040)
([#4049](#4049))
([f5b0142](f5b0142))
* allow "--containerize apptainer" to output apptainer format instead of
dockerfile ([#4030](#4030))
([f5cac30](f5cac30))
* apptainer command not recognized when singularity is absent
([#4010](#4010))
([b8162e2](b8162e2))
* capture stderr when tests fail
([#3995](#3995))
([97d74ba](97d74ba))
* **docs:** make Data-dependent conditional execution a complete example
([#4043](#4043))
([3a1d7f2](3a1d7f2))
* don't build the DAG when running unlock. Fixes
[#4000](#4000) and
[#198](#198)
([#4007](#4007))
([acf79fd](acf79fd))
* Ensure pixi tasks may be run as advertised
([#4046](#4046))
([88253c2](88253c2))
* fix checkpoint handling corner cases
([#3870](#3870) and
[#3559](#3559))
([#4015](#4015))
([63f4257](63f4257))
* issue 3642
([#4054](#4054))
([76e6fc2](76e6fc2))
* issue 3815
([#4026](#4026))
([b0eec96](b0eec96))
* logging None in shellcmd context causes error
([#4064](#4064))
([d0652cd](d0652cd))
* lookup function returns default value for empty DataFrame queries
([#4056](#4056))
([f71de97](f71de97))
* make `cache: omit-software` a rule specific property
([#4085](#4085))
([034a9e7](034a9e7))
* reduce number of tests leaving temporary files behind
([#4033](#4033))
([a3a1c97](a3a1c97))
* regression in dynamic resource handling
([#4038](#4038))
([f2c554a](f2c554a))
* somewhat shorter announce message
([#4080](#4080))
([57efc71](57efc71))


### Performance Improvements

* switch reretry with tenacity; decouple container classes (with Python
3.7 compat for old scripts) from rest of the codebase (enabling moving
to newer python versions)
([#4032](#4032))
([ffb19e7](ffb19e7))


### Documentation

* Add AI-assisted contributions policy to contributing guidelines
([#4051](#4051))
([dd70526](dd70526))
* **codebase:** Update & simplify plugin architecture section
([#4052](#4052))
([176cf63](176cf63))
* Correct workflow.source_path() description in documentation
([#4036](#4036))
([45883c5](45883c5))
* fixed wrong code example for collect() function
([#4037](#4037))
([5c85ed8](5c85ed8))
* Minor docs improvements
([#4089](#4089))
([29ea226](29ea226))
* switch to sphinx_design for tabs
([#3976](#3976))
([9674614](9674614))
* typo in the migration table breaking a pip install command
([#4024](#4024))
([66f9dda](66f9dda))

---
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