Create baseline commit for warning message

Author: phofl

pandas/errors/__init__.py

@@ -503,6 +503,19 @@ class ChainedAssignmentError(Warning):
 )
 
 
+_chained_assignment_warning_method_msg = (
+    "A value is trying to be set on a copy of a DataFrame or Series "
+    "through chained assignment using an inplace method.\n"
+    "The behavior will change in pandas 3.0. This inplace method will "
+    "never work because the intermediate object on which we are setting "
+    "values always behaves as a copy.\n\n"
+    "For example, when doing 'df[col].method(value, inplace=True)', try "
+    "using 'df.method({col: value}, inplace=True)' or "
+    "df[col] = df[col].method(value) instead, to perform "
+    "the operation inplace on the original object.\n\n"
+)
+
+
 class NumExprClobberingError(NameError):
     """
     Exception raised when trying to use a built-in numexpr name as a variable name.

scripts/validate_unwanted_patterns.py

@@ -50,6 +50,7 @@
     "_global_config",
     "_chained_assignment_msg",
     "_chained_assignment_method_msg",
+    "_chained_assignment_warning_method_msg",
     "_version_meson",
     # The numba extensions need this to mock the iloc object
     "_iLocIndexer",