DOC: Addition to pd.DataFrame.assign() docstring (#20085) (#20702)

Author: HannahFerch

pandas/core/frame.py

@@ -3177,7 +3177,8 @@ def insert(self, loc, column, value, allow_duplicates=False):
     def assign(self, **kwargs):
         r"""
         Assign new columns to a DataFrame, returning a new object
-        (a copy) with all the original columns in addition to the new ones.
+        (a copy) with the new columns added to the original ones.
+        Existing columns that are re-assigned will be overwritten.
 
         Parameters
         ----------