fix: Support polars 1.38

dataframely/_compat.py

@@ -80,10 +80,14 @@ class Dialect:  # type: ignore # noqa: N801
     from polars._typing import (  # type: ignore[attr-defined,unused-ignore]
         PartitioningScheme as PartitionSchemeOrSinkDirectory,
     )
-else:
+elif _polars_version_tuple < (1, 38):  # pragma: no cover
     from polars.io.partition import (  # type: ignore[no-redef,attr-defined,unused-ignore]
         _SinkDirectory as PartitionSchemeOrSinkDirectory,
     )
+else:
+    from polars.io.partition import (  # type: ignore[no-redef,attr-defined,unused-ignore]
+        PartitionBy as PartitionSchemeOrSinkDirectory,
+    )
 
 # ------------------------------------------------------------------------------------ #
 

dataframely/_storage/__init__.py

@@ -2,7 +2,6 @@
 # SPDX-License-Identifier: BSD-3-Clause
 
 from ._base import StorageBackend
+from ._fsspec import get_file_prefix
 
-__all__ = [
-    "StorageBackend",
-]
+__all__ = ["StorageBackend", "get_file_prefix"]

dataframely/_storage/_fsspec.py

@@ -0,0 +1,18 @@
+# Copyright (c) QuantCo 2025-2026
+# SPDX-License-Identifier: BSD-3-Clause
+
+from fsspec import AbstractFileSystem
+
+
+def get_file_prefix(fs: AbstractFileSystem) -> str:
+    match fs.protocol:
+        case "file":
+            return ""
+        case str():
+            return f"{fs.protocol}://"
+        case ["file", *_]:
+            return ""
+        case [str(proto), *_]:
+            return f"{proto}://"
+        case _:
+            raise ValueError(f"Unexpected fs.protocol: {fs.protocol}")

dataframely/_storage/parquet.py

@@ -7,6 +7,8 @@
 import polars as pl
 from fsspec import AbstractFileSystem, url_to_fs
 
+from dataframely._storage import get_file_prefix
+
 from ._base import (
     SerializedCollection,
     SerializedRules,
@@ -79,7 +81,9 @@ def sink_collection(
         fs: AbstractFileSystem = url_to_fs(path)[0]
         for key, lf in dfs.items():
             destination = (
-                fs.sep.join([path, key])
+                # Enforce that the path ends with a separator. Otherwise
+                # polars misbehaves on Windows.
+                fs.sep.join([path, key]) + fs.sep
                 if "partition_by" in kwargs
                 else fs.sep.join([path, f"{key}.parquet"])
             )
@@ -107,7 +111,9 @@ def write_collection(
         fs: AbstractFileSystem = url_to_fs(path)[0]
         for key, lf in dfs.items():
             destination = (
-                fs.sep.join([path, key])
+                # Enforce that the path ends with a separator. Otherwise
+                # polars misbehaves on Windows.
+                fs.sep.join([path, key]) + fs.sep
                 if "partition_by" in kwargs
                 else fs.sep.join([path, f"{key}.parquet"])
             )
@@ -155,15 +161,7 @@ def _collection_from_parquet(
                 if is_file:
                     collection_types.append(_read_serialized_collection(source_path))
                 else:
-                    prefix = (
-                        ""
-                        if fs.protocol == "file"
-                        else (
-                            f"{fs.protocol}://"
-                            if isinstance(fs.protocol, str)
-                            else f"{fs.protocol[0]}://"
-                        )
-                    )
+                    prefix = get_file_prefix(fs)
                     for file in fs.glob(fs.sep.join([source_path, "**", "*.parquet"])):
                         collection_types.append(
                             _read_serialized_collection(f"{prefix}{file}")

dataframely/testing/storage.py

@@ -10,6 +10,7 @@
 import dataframely as dy
 from dataframely import FailureInfo, Validation
 from dataframely._compat import deltalake
+from dataframely._storage import get_file_prefix
 from dataframely._storage.delta import _to_delta_table
 
 # ----------------------------------- Schema -------------------------------------------
@@ -190,19 +191,7 @@ def set_metadata(self, path: str, metadata: dict[str, Any]) -> None:
         metadata."""
 
     def _prefix_path(self, path: str, fs: AbstractFileSystem) -> str:
-        return f"{self._get_prefix(fs)}{path}"
-
-    @staticmethod
-    def _get_prefix(fs: AbstractFileSystem) -> str:
-        return (
-            ""
-            if fs.protocol == "file"
-            else (
-                f"{fs.protocol}://"
-                if isinstance(fs.protocol, str)
-                else f"{fs.protocol[0]}://"
-            )
-        )
+        return f"{get_file_prefix(fs)}{path}"
 
 
 class ParquetCollectionStorageTester(CollectionStorageTester):

pixi.toml

@@ -117,35 +117,35 @@ polars = "1.35.*"
 
 [feature.polars-latest.dependencies]
 # NOTE: Update docs/faq.md when updating this.
-polars = "1.36.*"
+polars = "1.38.*"
 
 [feature.nightly.tasks]
 install-polars-nightly = "pip install --pre --no-deps --upgrade --only-binary :all: polars polars-runtime-32"
 
 [environments]
 build = ["build"]
-default = ["dev", "lint", "optionals", "py314", "test", "polars-latest"]
+default = ["dev", "lint", "optionals", "polars-latest", "py314", "test"]
 docs = ["docs"]
 lint = { features = ["lint"], no-default-feature = true }
 nightly = ["nightly", "optionals", "test"]
 
 # Different python versions with the latest polars
-py310 = ["py310", "test", "polars-latest"]
-py311 = ["py311", "test", "polars-latest"]
-py312 = ["py312", "test", "polars-latest"]
-py313 = ["py313", "test", "polars-latest"]
-py314 = ["py314", "test", "polars-latest"]
+py310 = ["polars-latest", "py310", "test"]
+py311 = ["polars-latest", "py311", "test"]
+py312 = ["polars-latest", "py312", "test"]
+py313 = ["polars-latest", "py313", "test"]
+py314 = ["polars-latest", "py314", "test"]
 
 # Test with optional dependencies
-py314-optionals = ["optionals", "py314", "test", "polars-latest"]
+py314-optionals = ["optionals", "polars-latest", "py314", "test"]
 
 # Polars compatibility envs
-polars-minimal = ["py314", "test", "polars-minimal"]
 default-polars-minimal = [
   "dev",
   "lint",
   "optionals",
+  "polars-minimal",
   "py314",
   "test",
-  "polars-minimal",
 ]
+polars-minimal = ["polars-minimal", "py314", "test"]

tests/storage/test_fsspec.py

@@ -0,0 +1,26 @@
+# Copyright (c) QuantCo 2025-2026
+# SPDX-License-Identifier: BSD-3-Clause
+
+from typing import Any
+
+import pytest
+
+from dataframely._storage._fsspec import get_file_prefix
+
+
+class MockFS:
+    def __init__(self, protocol: Any) -> None:
+        self.protocol = protocol
+
+
+def test_get_file_prefix() -> None:
+    assert get_file_prefix(MockFS("file")) == ""
+    assert get_file_prefix(MockFS("s3")) == "s3://"
+    assert get_file_prefix(MockFS(["file", "whatever"])) == ""
+    assert get_file_prefix(MockFS(["s3", "whatever"])) == "s3://"
+
+
+@pytest.mark.parametrize("protocol", [5, None, [5]])
+def test_get_file_prefix_invalid(protocol: Any) -> None:
+    with pytest.raises(ValueError):
+        assert 1 == get_file_prefix(MockFS(protocol))