cast is working!!!

narwhals/pandas_like/expr.py

@@ -66,7 +66,10 @@ def from_column_names(
             implementation=implementation,
         )
 
-    def cast(self, dtype: DType) -> Self:  # type: ignore[override]
+    def cast(
+        self,
+        dtype: DType,  # type: ignore[override]
+    ) -> Self:
         return register_expression_call(self, "cast", dtype)
 
     def __eq__(self, other: Expr | Any) -> Self:  # type: ignore[override]

narwhals/pandas_like/utils.py

@@ -359,12 +359,36 @@ def translate_dtype(dtype: Any) -> DType:
     raise TypeError(msg)
 
 
-def reverse_translate_dtype(dtype: DType) -> Any:
+def isinstance_or_issubclass(obj: Any, cls: Any) -> bool:
+    return isinstance(obj, cls) or issubclass(obj, cls)
+
+
+def reverse_translate_dtype(dtype: DType | type[DType]) -> Any:
     from narwhals.pandas_like import dtypes
 
-    if isinstance(dtype, dtypes.Int64):
-        return "int64"
-    if isinstance(dtype, dtypes.Float32) or issubclass(dtype, dtypes.Float32):
+    if isinstance_or_issubclass(dtype, dtypes.Float64):
+        return "float64"
+    if isinstance_or_issubclass(dtype, dtypes.Float32):
         return "float32"
+    if isinstance_or_issubclass(dtype, dtypes.Int64):
+        return "int64"
+    if isinstance_or_issubclass(dtype, dtypes.Int32):
+        return "int32"
+    if isinstance_or_issubclass(dtype, dtypes.Int16):
+        return "int16"
+    if isinstance_or_issubclass(dtype, dtypes.UInt8):
+        return "uint8"
+    if isinstance_or_issubclass(dtype, dtypes.UInt64):
+        return "uint64"
+    if isinstance_or_issubclass(dtype, dtypes.UInt32):
+        return "uint32"
+    if isinstance_or_issubclass(dtype, dtypes.UInt16):
+        return "uint16"
+    if isinstance_or_issubclass(dtype, dtypes.UInt8):
+        return "uint8"
+    if isinstance_or_issubclass(dtype, dtypes.String):
+        return "object"
+    if isinstance_or_issubclass(dtype, dtypes.Bool):
+        return "bool"
     msg = f"Unknown dtype: {dtype}"
     raise TypeError(msg)

narwhals/spec/__init__.py

@@ -15,6 +15,9 @@ class Expr(Protocol):
     def alias(self, name: str) -> Self:
         ...
 
+    def cast(self, dtype: DType) -> Self:
+        ...
+
     def __and__(self, other: Any) -> Expr:
         ...