BUG: memory_usage method with deep of StringArray is wrong

Author: kotamatsuoka

pandas/core/arrays/string_.py

@@ -289,6 +289,12 @@ def value_counts(self, dropna=False):
 
         return value_counts(self._ndarray, dropna=dropna).astype("Int64")
 
+    def memory_usage(self, deep=False):
+        result = self._ndarray.nbytes
+        if deep:
+            return result + lib.memory_usage_of_objects(self._ndarray)
+        return result
+
     # Override parent because we have different return types.
     @classmethod
     def _create_arithmetic_method(cls, op):

pandas/tests/extension/test_string.py

@@ -85,6 +85,14 @@ class TestMethods(base.BaseMethodsTests):
     def test_value_counts(self, all_data, dropna):
         return super().test_value_counts(all_data, dropna)
 
+    def test_memory_usage(self, data):
+        # GH 33963
+        series = pd.Series(data, dtype="string")
+
+        assert (
+            0 < series.nbytes <= series.memory_usage() < series.memory_usage(deep=True)
+        )
+
 
 class TestCasting(base.BaseCastingTests):
     pass