DuckDBPyRelation.aggregate has incorrect typing #209

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1. m15a

   added

   needs triage

   on Dec 5, 2025
2. evertlammerts

   added

   stubs

   and removed

   needs triage

   on Dec 6, 2025
3. evertlammerts

   added a commit that references this issue on Jan 6, 2026

   Fix : aggregate method typing to accept list of expressions (#246)

   ...

   This issue will close once commit 45fb522 is merged into the 'v2.0-cyanoptera' branch.

   45fb522
4. OutSquareCapital commented on Feb 12, 2026

   

   OutSquareCapital

   on Feb 12, 2026

   Last edited by OutSquareCapital

   Contributor

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   I stumbled upon this problem and took a look at the merged pull request, however unfortunately the type is still too narrow.
   It should be Iterable[Expression | str] instead of list[Expression].
   I'm not sure why list[int] don't crash or even what it does, but it does work too apparently.

   see below:

   Code

   from functools import partial
   
   import duckdb
   import polars as pl
   import pyochain as pc
   
   
   def _get_rel() -> duckdb.DuckDBPyRelation:
       df = pl.DataFrame({"foo": ["a"], "bar": [1]})
       return duckdb.from_arrow(df)
   
   
   def _try_agg(rel: duckdb.DuckDBPyRelation, arg: object) -> None:
       def _name() -> str:
           repr = f"{type(arg).__name__}"
           if isinstance(arg, list):
               repr += f"[{type(arg[0]).__name__}]"
           return f"*{repr}*"
   
       try:
           res = rel.aggregate(arg).fetchone()
           return print(f"- **Ok** with arg {_name()}: `{res}`")
       except Exception as e:
           return print(f"- **Error** with arg {_name()}: `{e}`")
   
   
   def main() -> None:
       data = ["foo", "bar"]
       # Generator of ColumExpressions
       col_args = (duckdb.ColumnExpression(str(x)) for x in data)
       # custom object, Iterator protocol implemented.
       iter_arg = pc.Iter(data)
   
       col = duckdb.ColumnExpression("foo")
       tst_on = partial(_try_agg, _get_rel())
       tst_on(data)
       tst_on(col_args)
       tst_on(iter_arg)
       tst_on(6)
       tst_on([6])
       tst_on("foo")
       tst_on([col])
       tst_on(col)
   
   
   if __name__ == "__main__":
       main()

   Output

   • Ok with arg list[str]: ('a', 1)
   • Ok with arg generator: ('a', 1)
   • Ok with arg Iter: ('a', 1)
   • Error with arg int: Invalid Input Error: Please provide either a string or list of Expression objects, not <class 'int'>
   • Ok with arg list[int]: (6,)
   • Ok with arg str: ('a',)
   • Ok with arg list[Expression]: ('a',)
   • Error with arg Expression: Invalid Input Error: Please provide either a string or list of Expression objects, not <class '_duckdb.Expression'>
5. evertlammerts commented on Feb 17, 2026

   

   evertlammerts

   on Feb 17, 2026

   Member

   More actions

   Fixed in #323. Widened aggr_expr on DuckDBPyRelation.aggregate() from Expression | str | list[Expression] to str | Expression | list[Expression | str].
6. evertlammerts

   closed this as completedon Feb 17, 2026
7. OutSquareCapital commented on Feb 17, 2026

   

   OutSquareCapital

   on Feb 17, 2026

   Contributor

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   Sorry to be pedantic but again list is wrong here as I showed above.
   It's too narrow, and I'm very rarely using plain lists in my day-to-day usage.
   So either I use cast and type ignore everywhere, or I inefficiently call list on my Iterator/Sequence/tuple before passing it to the method.
8. evertlammerts

   added a commit that references this issue on Feb 17, 2026

   Fix multiple stub issues (#323)

   ...

   cdf800e