added comment, pointed back to the issue

Author: debnathshoham

pandas/io/parsers/python_parser.py

@@ -81,6 +81,7 @@ def __init__(self, f: FilePathOrBuffer | list, **kwds):
         self.verbose = kwds["verbose"]
         self.converters = kwds["converters"]
 
+        # GH 42462 : dtype dict parameter changes with duplicate columns in input data
         if isinstance(kwds["dtype"], dict):
             self.dtype = kwds["dtype"].copy()
         else: