pl.map_groups with return_dtype=pl.Object causes pyo3_runtime.PanicException: object dtype not supported in Series.iter #22814
Description
Checks
- I have checked that this issue has not already been reported.
- I have confirmed this bug exists on the latest version of Polars.
Reproducible example
import polars as pl
class CustomObject:
pass
df = pl.DataFrame({
"id": [1, 2, 3, 4],
"objects": [ CustomObject(), CustomObject(), CustomObject(), CustomObject() ],
})
df = df.group_by("id").agg(
pl.map_groups([pl.col("objects")], lambda x: x[0], return_dtype=pl.Object).alias("first_object"))
print(df)Log output
Issue description
Using pl.map_groups with return_dtype=pl.Object works with polars 1.27.1. However, using polars 1.28.1 or later, I get the following error:
$RUST_BACKTRACE=full POLARS_VERBOSE=1 python polars-bug-report.py
keys/aggregates are not partitionable: running default HASH AGGREGATION
thread '<unnamed>' panicked at crates/polars-core/src/series/iterator.rs:84:9:
object dtype not supported in Series.iter
stack backtrace:
0: 0x138d27088 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::ha26fa7c0f8baf7a4
1: 0x1356bbc80 - core::fmt::write::h8eff90b819ed25ac
2: 0x138d251c4 - std::io::Write::write_fmt::hc3767759e8313866
3: 0x138d26f28 - std::sys::backtrace::BacktraceLock::print::h5ab5bdfc8c7040c6
4: 0x138d259d0 - std::panicking::default_hook::h2517e562906dc496
5: 0x138d24fd0 - std::panicking::rust_panic_with_hook::hdf5ea4a7520fe9b8
6: 0x138d55c60 - std::panicking::begin_panic_handler::{{closure}}::h7e667cf4bf22d5a9
7: 0x138d55bf8 - std::sys::backtrace::__rust_end_short_backtrace::h6ac6505b1a15fed1
8: 0x138d58520 - __rustc[e5679b3fd213e125]::rust_begin_unwind
9: 0x138e8ae78 - core::panicking::panic_fmt::h0d9b963f0cbbd487
10: 0x135de2160 - polars_core::series::iterator::<impl polars_core::series::Series>::iter::hd3b9b60a26bcea7d
11: 0x135de19a4 - polars_core::fmt::<impl polars_core::series::Series>::fmt_list::ha53e1e28eda4e628
12: 0x135de2e4c - polars_core::fmt::<impl core::fmt::Display for polars_core::datatypes::any_value::AnyValue>::fmt::h7db1bdbe0423a9c7
13: 0x135e07f64 - polars_core::datatypes::any_value::AnyValue::str_value::h7ec314145cbb1bdd
14: 0x1364ad8b8 - polars_core::fmt::<impl core::fmt::Display for polars_core::frame::DataFrame>::fmt::he2f1ccfbfc85ddd5
15: 0x1356bbc80 - core::fmt::write::h8eff90b819ed25ac
16: 0x13566df38 - alloc::fmt::format::format_inner::ha99af07c905693b7
17: 0x137ceb2e4 - polars_python::dataframe::general::<impl polars_python::dataframe::PyDataFrame>::__pymethod_as_str__::hfbdc063217bfad4b
18: 0x13822dd88 - pyo3::impl_::trampoline::trampoline::h1954118760425091
19: 0x137c81904 - polars_python::dataframe::general::_::__INVENTORY::trampoline::h4f8bddb385110bbd
20: 0x103313cb0 - _method_vectorcall_NOARGS
21: 0x103462654 - __PyEval_EvalFrameDefault
22: 0x10339a91c - _vectorcall_method
23: 0x10339d97c - _slot_tp_str
24: 0x103375710 - _PyObject_Str
25: 0x103326f70 - _PyFile_WriteObject
26: 0x103454aa0 - _builtin_print
27: 0x1033708d4 - _cfunction_vectorcall_FASTCALL_KEYWORDS
28: 0x103462654 - __PyEval_EvalFrameDefault
29: 0x103456e64 - _PyEval_EvalCode
30: 0x1034d7ed8 - _run_mod
31: 0x1034d6f40 - _pyrun_file
32: 0x1034d5e1c - __PyRun_SimpleFileObject
33: 0x1034d59e0 - __PyRun_AnyFileObject
34: 0x103505858 - _pymain_run_file_obj
35: 0x1035055d0 - _pymain_run_file
36: 0x10350489c - _Py_RunMain
37: 0x103504f7c - _pymain_main
38: 0x103505098 - _Py_BytesMain
Traceback (most recent call last):
File "/project/polars-bug-report.py", line 11, in <module>
print(df)
File "/project/.venv/lib/python3.12/site-packages/polars/dataframe/frame.py", line 1199, in __str__
return self._df.as_str()
^^^^^^^^^^^^^^^^^
pyo3_runtime.PanicException: object dtype not supported in Series.iter
Expected behavior
Using polars 1.27.1, I get the following output:
$ RUST_BACKTRACE=full POLARS_VERBOSE=1 python polars-bug-report.py
keys/aggregates are not partitionable: running default HASH AGGREGATION
shape: (4, 2)
┌─────┬─────────────────────────────────┐
│ id ┆ first_object │
│ --- ┆ --- │
│ i64 ┆ object │
╞═════╪═════════════════════════════════╡
│ 1 ┆ <__main__.CustomObject object … │
│ 3 ┆ <__main__.CustomObject object … │
│ 2 ┆ <__main__.CustomObject object … │
│ 4 ┆ <__main__.CustomObject object … │
└─────┴─────────────────────────────────┘
Installed versions
--------Version info---------
Polars: 1.28.1
Index type: UInt32
Platform: macOS-15.4.1-arm64-arm-64bit
Python: 3.12.9 (v3.12.9:fdb81425a9a, Feb 4 2025, 12:21:36) [Clang 13.0.0 (clang-1300.0.29.30)]
LTS CPU: False
----Optional dependencies----
Azure CLI <not installed>
adbc_driver_manager <not installed>
altair <not installed>
azure.identity <not installed>
boto3 <not installed>
cloudpickle <not installed>
connectorx <not installed>
deltalake <not installed>
fastexcel <not installed>
fsspec <not installed>
gevent <not installed>
google.auth <not installed>
great_tables <not installed>
matplotlib <not installed>
numpy <not installed>
openpyxl <not installed>
pandas <not installed>
polars_cloud <not installed>
pyarrow <not installed>
pydantic <not installed>
pyiceberg <not installed>
sqlalchemy <not installed>
torch <not installed>
xlsx2csv <not installed>
xlsxwriter <not installed>
And my polars 1.27.1 version info:
--------Version info---------
Polars: 1.27.1
Index type: UInt32
Platform: macOS-15.4.1-arm64-arm-64bit
Python: 3.12.9 (v3.12.9:fdb81425a9a, Feb 4 2025, 12:21:36) [Clang 13.0.0 (clang-1300.0.29.30)]
LTS CPU: False
----Optional dependencies----
Azure CLI <not installed>
adbc_driver_manager <not installed>
altair <not installed>
azure.identity <not installed>
boto3 <not installed>
cloudpickle <not installed>
connectorx <not installed>
deltalake <not installed>
fastexcel <not installed>
fsspec <not installed>
gevent <not installed>
google.auth <not installed>
great_tables <not installed>
matplotlib <not installed>
numpy <not installed>
openpyxl <not installed>
pandas <not installed>
polars_cloud <not installed>
pyarrow <not installed>
pydantic <not installed>
pyiceberg <not installed>
sqlalchemy <not installed>
torch <not installed>
xlsx2csv <not installed>
xlsxwriter <not installed>