Support dataframe creation from mapping of mapping

Author: mrkn

pandas/core/frame.py

@@ -1735,7 +1735,7 @@ def __rmatmul__(self, other) -> DataFrame:
     @classmethod
     def from_dict(
         cls,
-        data: dict,
+        data: Mapping,
         orient: FromDictOrient = "columns",
         dtype: Dtype | None = None,
         columns: Axes | None = None,
@@ -1748,7 +1748,7 @@ def from_dict(
 
         Parameters
         ----------
-        data : dict
+        data : Mapping
             Of the form {field : array-like} or {field : dict}.
         orient : {'columns', 'index', 'tight'}, default 'columns'
             The "orientation" of the data. If the keys of the passed dict

pandas/core/internals/construction.py

@@ -77,7 +77,6 @@
 if TYPE_CHECKING:
     from collections.abc import (
         Hashable,
-        Mapping,
         Sequence,
     )
 
@@ -348,7 +347,7 @@ def _check_values_indices_shape_match(
 
 
 def dict_to_mgr(
-    data: Mapping,
+    data: abc.Mapping,
     index,
     columns,
     *,
@@ -537,7 +536,7 @@ def _homogenize(
             refs.append(val._references)
             val = val._values
         else:
-            if isinstance(val, dict):
+            if isinstance(val, abc.Mapping):
                 # GH#41785 this _should_ be equivalent to (but faster than)
                 #  val = Series(val, index=index)._values
                 if oindex is None:
@@ -579,7 +578,7 @@ def _extract_index(data) -> Index:
         if isinstance(val, ABCSeries):
             have_series = True
             indexes.append(val.index)
-        elif isinstance(val, dict):
+        elif isinstance(val, abc.Mapping):
             have_dicts = True
             indexes.append(list(val.keys()))
         elif is_list_like(val) and getattr(val, "ndim", 1) == 1:

pandas/tests/frame/constructors/test_from_dict.py

@@ -146,6 +146,18 @@ def test_constructor_from_mapping(self):
         result = DataFrame.from_dict(DictWrapper({"A": idx, "B": dr}))
         tm.assert_frame_equal(result, expected)
 
+    def test_constructor_from_mapping_of_mapping(self):
+        data = DictWrapper(
+            {
+                "a": DictWrapper({"x": 1, "y": 2}),
+                "b": DictWrapper({"x": 3, "y": 4}),
+                "c": DictWrapper({"x": 5, "y": 6}),
+            }
+        )
+        expected = DataFrame(data)
+        result = DataFrame.from_dict(data)
+        tm.assert_frame_equal(result, expected)
+
     def test_from_dict_columns_parameter(self):
         # GH#18529
         # Test new columns parameter for from_dict that was added to make

pandas/tests/frame/test_constructors.py

@@ -2932,6 +2932,31 @@ def test_from_mapping(self):
         tm.assert_series_equal(df["A"], Series(idx, name="A"))
         tm.assert_series_equal(df["B"], Series(dr, name="B"))
 
+    def test_from_mapping_of_dict(self):
+        data = {
+            "a": {"x": 1, "y": 2},
+            "b": {"x": 3, "y": 4},
+            "c": {"x": 5, "y": 6},
+        }
+        expected = DataFrame(data)
+
+        # construction
+        result = DataFrame(DictWrapper(data))
+        tm.assert_frame_equal(result, expected)
+
+    def test_from_mapping_of_mapping(self):
+        data = {
+            "a": {"x": 1, "y": 2},
+            "b": {"x": 3, "y": 4},
+            "c": {"x": 5, "y": 6},
+        }
+        expected = DataFrame(data)
+
+        # construction
+        wrapped = DictWrapper({k: DictWrapper(v) for k, v in data.items()})
+        result = DataFrame(wrapped)
+        tm.assert_frame_equal(result, expected)
+
     def test_from_mapping_list(self):
         idx = Index(date_range("20130101", periods=3, tz="US/Eastern"), name="foo")
         dr = date_range("20130110", periods=3)