revert internal method

Author: topper-123

pandas/core/base.py

@@ -1038,9 +1038,6 @@ def nunique(self, dropna: bool = True) -> int:
             n -= 1
         return n
 
-    def _is_unique(self) -> bool:
-        return self.nunique(dropna=False) == len(self)
-
     @property
     def is_unique(self) -> bool:
         """
@@ -1050,7 +1047,7 @@ def is_unique(self) -> bool:
         -------
         bool
         """
-        return self._is_unique()
+        return self.nunique(dropna=False) == len(self)
 
     @property
     def is_monotonic(self) -> bool:

pandas/core/frame.py

@@ -5223,7 +5223,7 @@ def is_unique(
             self = self[subset]
 
         if len(self.columns):
-            return self.apply(Series._is_unique)
+            return self.apply(lambda x: x.is_unique)
         else:
             return self._constructor_sliced(dtype=bool)