chore(typing): SparkLikeExpr properties

narwhals/_spark_like/expr.py

@@ -24,6 +24,7 @@
 
 if TYPE_CHECKING:
     from pyspark.sql import Column
+    from pyspark.sql import Window
     from typing_extensions import Self
 
     from narwhals._spark_like.dataframe import SparkLikeLazyFrame
@@ -78,7 +79,11 @@ def func(df: SparkLikeLazyFrame) -> Sequence[Column]:
         )
 
     @property
-    def _F(self: Self) -> Any:  # noqa: N802
+    def _F(self: Self):  # type: ignore[no-untyped-def] # noqa: ANN202, N802
+        if TYPE_CHECKING:
+            from pyspark.sql import functions
+
+            return functions
         if self._implementation is Implementation.SQLFRAME:
             from sqlframe.base.session import _BaseSession
 
@@ -91,7 +96,11 @@ def _F(self: Self) -> Any:  # noqa: N802
         return functions
 
     @property
-    def _native_dtypes(self: Self) -> Any:
+    def _native_dtypes(self: Self):  # type: ignore[no-untyped-def] # noqa: ANN202
+        if TYPE_CHECKING:
+            from pyspark.sql import types
+
+            return types
         if self._implementation is Implementation.SQLFRAME:
             from sqlframe.base.session import _BaseSession
 
@@ -104,7 +113,7 @@ def _native_dtypes(self: Self) -> Any:
         return types
 
     @property
-    def _Window(self: Self) -> Any:  # noqa: N802
+    def _Window(self: Self) -> type[Window]:  # noqa: N802
         if self._implementation is Implementation.SQLFRAME:
             from sqlframe.base.session import _BaseSession
 

narwhals/_spark_like/expr_str.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
+from functools import partial
 from typing import TYPE_CHECKING
-from typing import overload
 
 if TYPE_CHECKING:
     from pyspark.sql import Column
@@ -107,47 +107,29 @@ def to_lowercase(self: Self) -> SparkLikeExpr:
         )
 
     def to_datetime(self: Self, format: str | None) -> SparkLikeExpr:  # noqa: A002
-        is_naive = (
-            format is not None
-            and "%s" not in format
-            and "%z" not in format
-            and "Z" not in format
-        )
-        function = (
-            self._compliant_expr._F.to_timestamp_ntz
-            if is_naive
-            else self._compliant_expr._F.to_timestamp
-        )
-        pyspark_format = strptime_to_pyspark_format(format)
-        format = (
-            self._compliant_expr._F.lit(pyspark_format) if is_naive else pyspark_format
-        )
+        F = self._compliant_expr._F  # noqa: N806
+        if not format:
+            function = F.to_timestamp
+        elif is_naive_format(format):
+            function = partial(
+                F.to_timestamp_ntz, format=F.lit(strptime_to_pyspark_format(format))
+            )
+        else:
+            format = strptime_to_pyspark_format(format)
+            function = partial(F.to_timestamp, format=format)
         return self._compliant_expr._from_call(
-            lambda _input: function(
-                self._compliant_expr._F.replace(
-                    _input,
-                    self._compliant_expr._F.lit("T"),
-                    self._compliant_expr._F.lit(" "),
-                ),
-                format=format,
-            ),
+            lambda _input: function(F.replace(_input, F.lit("T"), F.lit(" "))),
             "to_datetime",
         )
 
 
-@overload
-def strptime_to_pyspark_format(format: None) -> None: ...
-
-
-@overload
-def strptime_to_pyspark_format(format: str) -> str: ...
+def is_naive_format(format: str) -> bool:  # noqa: A002
+    return not any(x in format for x in ("%s", "%z", "Z"))
 
 
-def strptime_to_pyspark_format(format: str | None) -> str | None:  # noqa: A002
+def strptime_to_pyspark_format(format: str) -> str:  # noqa: A002
     """Converts a Python strptime datetime format string to a PySpark datetime format string."""
     # Mapping from Python strptime format to PySpark format
-    if format is None:
-        return None
 
     # see https://spark.apache.org/docs/latest/sql-ref-datetime-pattern.html
     # and https://docs.python.org/3/library/datetime.html#strftime-strptime-behavior