From 83f562e2c2d57e1b0c8c570a84c4405c1ddbc198 Mon Sep 17 00:00:00 2001
From: Ambuj Pawar <pawar.ambuj@gmail.com>
Date: Mon, 24 Oct 2022 23:06:49 +0200
Subject: [PATCH] =?UTF-8?q?Backport=20PR=20#48890:=20ERR:=20Improve=20erro?=
 =?UTF-8?q?r=20message=20when=20assigning=20a=20complete=20row=20using=20'?=
 =?UTF-8?q?at'=20m=E2=80=A6?=
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---
 pandas/core/frame.py             |  8 ++++++++
 pandas/tests/indexing/test_at.py | 18 ++++++++++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index b525bf6f57e88..d3116f83d58cb 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -86,6 +86,7 @@
     function as nv,
     np_percentile_argname,
 )
+from pandas.errors import InvalidIndexError
 from pandas.util._decorators import (
     Appender,
     Substitution,
@@ -4220,6 +4221,13 @@ def _set_value(
                 self.loc[index, col] = value
             self._item_cache.pop(col, None)
 
+        except InvalidIndexError as ii_err:
+            # GH48729: Seems like you are trying to assign a value to a
+            # row when only scalar options are permitted
+            raise InvalidIndexError(
+                f"You can only assign a scalar value not a {type(value)}"
+            ) from ii_err
+
     def _ensure_valid_index(self, value) -> None:
         """
         Ensure that if we don't have an index, that we can create one from the
diff --git a/pandas/tests/indexing/test_at.py b/pandas/tests/indexing/test_at.py
index 1e502ca70189a..adbc0e2f8127a 100644
--- a/pandas/tests/indexing/test_at.py
+++ b/pandas/tests/indexing/test_at.py
@@ -197,8 +197,12 @@ def test_at_frame_raises_key_error2(self, indexer_al):
     def test_at_frame_multiple_columns(self):
         # GH#48296 - at shouldn't modify multiple columns
         df = DataFrame({"a": [1, 2], "b": [3, 4]})
-        with pytest.raises(InvalidIndexError, match=r"slice\(None, None, None\)"):
-            df.at[5] = [6, 7]
+        new_row = [6, 7]
+        with pytest.raises(
+            InvalidIndexError,
+            match=f"You can only assign a scalar value not a \\{type(new_row)}",
+        ):
+            df.at[5] = new_row
 
     def test_at_getitem_mixed_index_no_fallback(self):
         # GH#19860
@@ -220,3 +224,13 @@ def test_at_categorical_integers(self):
             for key in [0, 1]:
                 with pytest.raises(KeyError, match=str(key)):
                     df.at[key, key]
+
+    def test_at_applied_for_rows(self):
+        # GH#48729 .at should raise InvalidIndexError when assigning rows
+        df = DataFrame(index=["a"], columns=["col1", "col2"])
+        new_row = [123, 15]
+        with pytest.raises(
+            InvalidIndexError,
+            match=f"You can only assign a scalar value not a \\{type(new_row)}",
+        ):
+            df.at["a"] = new_row