silence infer_objects warning for object backed string type

Author: lithomas1

pandas/core/frame.py

@@ -923,7 +923,12 @@ def __init__(
 
         NDFrame.__init__(self, mgr)
 
-        if original_dtype is None and is_pandas_object and data_dtype == np.object_:
+        if (
+            original_dtype is None
+            and is_pandas_object
+            and data_dtype == np.object_
+            and self.dtypes.iloc[0] != "str"
+        ):
             if self.dtypes.iloc[0] != data_dtype:
                 warnings.warn(
                     "Dtype inference on a pandas object "

pandas/core/indexes/base.py

@@ -575,7 +575,13 @@ def __new__(
 
         arr = klass._ensure_array(arr, arr.dtype, copy=False)
         result = klass._simple_new(arr, name, refs=refs)
-        if dtype is None and is_pandas_object and data_dtype == np.object_:
+        # TODO: also verify this check
+        if (
+            dtype is None
+            and is_pandas_object
+            and data_dtype == np.object_
+            and result.dtype != "str"
+        ):
             if result.dtype != data_dtype:
                 warnings.warn(
                     "Dtype inference on a pandas object "

pandas/core/series.py

@@ -593,7 +593,13 @@ def __init__(
         self.name = name
         self._set_axis(0, index)
 
-        if original_dtype is None and is_pandas_object and data_dtype == np.object_:
+        # TODO: verify we're silencing the warning correctly here
+        if (
+            original_dtype is None
+            and is_pandas_object
+            and data_dtype == np.object_
+            and self.dtype != "str"
+        ):
             if self.dtype != data_dtype:
                 warnings.warn(
                     "Dtype inference on a pandas object "