REF: implement construct_2d_arraylike_from_scalar (#38583)

Author: jbrockmendel

pandas/core/dtypes/cast.py

@@ -1526,6 +1526,28 @@ def find_common_type(types: List[DtypeObj]) -> DtypeObj:
     return np.find_common_type(types, [])
 
 
+def construct_2d_arraylike_from_scalar(
+    value: Scalar, length: int, width: int, dtype: np.dtype, copy: bool
+) -> np.ndarray:
+
+    if dtype.kind in ["m", "M"]:
+        value = maybe_unbox_datetimelike(value, dtype)
+
+    # Attempt to coerce to a numpy array
+    try:
+        arr = np.array(value, dtype=dtype, copy=copy)
+    except (ValueError, TypeError) as err:
+        raise TypeError(
+            f"DataFrame constructor called with incompatible data and dtype: {err}"
+        ) from err
+
+    if arr.ndim != 0:
+        raise ValueError("DataFrame constructor not properly called!")
+
+    shape = (length, width)
+    return np.full(shape, arr)
+
+
 def construct_1d_arraylike_from_scalar(
     value: Scalar, length: int, dtype: Optional[DtypeObj]
 ) -> ArrayLike:

pandas/core/frame.py

@@ -85,14 +85,14 @@
 
 from pandas.core.dtypes.cast import (
     construct_1d_arraylike_from_scalar,
+    construct_2d_arraylike_from_scalar,
     find_common_type,
     infer_dtype_from_scalar,
     invalidate_string_dtypes,
     maybe_box_datetimelike,
     maybe_convert_platform,
     maybe_downcast_to_dtype,
     maybe_infer_to_datetimelike,
-    maybe_unbox_datetimelike,
     validate_numeric_casting,
 )
 from pandas.core.dtypes.common import (
@@ -595,31 +595,17 @@ def __init__(
 
             # For data is a scalar extension dtype
             if is_extension_array_dtype(dtype):
+                # TODO(EA2D): special case not needed with 2D EAs
 
                 values = [
                     construct_1d_arraylike_from_scalar(data, len(index), dtype)
                     for _ in range(len(columns))
                 ]
                 mgr = arrays_to_mgr(values, columns, index, columns, dtype=None)
             else:
-                if dtype.kind in ["m", "M"]:
-                    data = maybe_unbox_datetimelike(data, dtype)
-
-                # Attempt to coerce to a numpy array
-                try:
-                    arr = np.array(data, dtype=dtype, copy=copy)
-                except (ValueError, TypeError) as err:
-                    exc = TypeError(
-                        "DataFrame constructor called with "
-                        f"incompatible data and dtype: {err}"
-                    )
-                    raise exc from err
-
-                if arr.ndim != 0:
-                    raise ValueError("DataFrame constructor not properly called!")
-
-                shape = (len(index), len(columns))
-                values = np.full(shape, arr)
+                values = construct_2d_arraylike_from_scalar(
+                    data, len(index), len(columns), dtype, copy
+                )
 
                 mgr = init_ndarray(
                     values, index, columns, dtype=values.dtype, copy=False