refactor(python): Add TypeGuard to is_polars_dtype util (#16065)

py-polars/polars/datatypes/convert.py

@@ -68,6 +68,10 @@
 
     from polars.type_aliases import PolarsDataType, PythonDataType, SchemaDict, TimeUnit
 
+    if sys.version_info >= (3, 10):
+        from typing import TypeGuard
+    else:
+        from typing_extensions import TypeGuard
 
 PY_STR_TO_DTYPE: SchemaDict = {
     "float": Float64,
@@ -139,7 +143,9 @@ def _map_py_type_to_dtype(
     raise TypeError(msg)
 
 
-def is_polars_dtype(dtype: Any, *, include_unknown: bool = False) -> bool:
+def is_polars_dtype(
+    dtype: Any, *, include_unknown: bool = False
+) -> TypeGuard[PolarsDataType]:
     """Indicate whether the given input is a Polars dtype, or dtype specialization."""
     try:
         if dtype == Unknown:

py-polars/polars/functions/col.py

@@ -29,7 +29,7 @@ def _create_col(
             return wrap_expr(plr.cols(names_str))
         elif is_polars_dtype(name):
             dtypes = [name]
-            dtypes.extend(more_names)
+            dtypes.extend(more_names)  # type: ignore[arg-type]
             return wrap_expr(plr.dtype_cols(dtypes))
         else:
             msg = (

py-polars/polars/selectors.py

@@ -223,7 +223,7 @@ def _combine_as_selector(
     if names:
         selected.append(by_name(*names))
     if dtypes:
-        selected.append(by_dtype(*dtypes))  # type: ignore[arg-type]
+        selected.append(by_dtype(*dtypes))
     if regexes:
         selected.append(
             matches(
@@ -579,7 +579,7 @@ def by_dtype(
     all_dtypes: list[PolarsDataType] = []
     for tp in dtypes:
         if is_polars_dtype(tp):
-            all_dtypes.append(tp)  # type: ignore[arg-type]
+            all_dtypes.append(tp)
         elif isinstance(tp, Collection):
             for t in tp:
                 if not is_polars_dtype(t):