speed up?

narwhals/pandas_like/dataframe.py

@@ -30,21 +30,20 @@ def __init__(
         dataframe: Any,
         *,
         implementation: str,
-        validate: bool = True,
     ) -> None:
-        if validate:
-            self._validate_columns(dataframe.columns)
+        self._validate_columns(dataframe.columns)
         self._dataframe = dataframe
         self._implementation = implementation
 
     def _validate_columns(self, columns: Sequence[str]) -> None:
-        counter = collections.Counter(columns)
-        for col, count in counter.items():
-            if count > 1:
-                msg = f"Expected unique column names, got {col!r} {count} time(s)"
-                raise ValueError(
-                    msg,
-                )
+        if len(columns) != len(set(columns)):
+            counter = collections.Counter(columns)
+            for col, count in counter.items():
+                if count > 1:
+                    msg = f"Expected unique column names, got {col!r} {count} time(s)"
+                    raise ValueError(
+                        msg,
+                    )
 
     def _validate_booleanness(self) -> None:
         if not (
@@ -59,7 +58,6 @@ def _from_dataframe(self, df: Any) -> Self:
         return self.__class__(
             df,
             implementation=self._implementation,
-            validate=False,
         )
 
     def __getitem__(self, column_name: str) -> PandasSeries: