feat(python): return Datetime/Duration with appropriate timeunit when…

… inferring from pytype (#5127)

py-polars/polars/datatypes.py

@@ -410,8 +410,8 @@ def __hash__(self) -> int:
     str: Utf8,
     bool: Boolean,
     date: Date,
-    datetime: Datetime,
-    timedelta: Duration,
+    datetime: Datetime("us"),
+    timedelta: Duration("us"),
     time: Time,
     list: List,
     tuple: List,

py-polars/tests/unit/test_datatypes.py

@@ -2,6 +2,7 @@
 
 import inspect
 import pickle
+from datetime import datetime, timedelta
 
 import polars as pl
 from polars import datatypes
@@ -30,6 +31,14 @@ def test_dtype_temporal_units() -> None:
     assert pl.Datetime("ms") != pl.Datetime("ns")
     assert pl.Duration("ns") != pl.Duration("us")
 
+    # check timeunit from pytype
+    for inferred_dtype, expected_dtype in (
+        (datatypes.py_type_to_dtype(datetime), pl.Datetime),
+        (datatypes.py_type_to_dtype(timedelta), pl.Duration),
+    ):
+        assert inferred_dtype == expected_dtype
+        assert inferred_dtype.tu == "us"  # type: ignore[union-attr]
+
 
 def test_get_idx_type() -> None:
     assert datatypes.get_idx_type() == datatypes.UInt32