Thanks @serhiy.storchaka . I looked into the code and it seems the resolution is done in `search_function` at Lib/encodings/__init__.py . It seems that encoding is normalized using some logic and then we use the normalized encoding to check against aliases which is the dictionary where I have added the alias. If it's not found then '.' is replaced with '_' to check again. I hope this is the place where I need to check if aliased_encoding is None after both attempts and norm_encoding is all digits then prepend "cp" to norm_encoding to check again against `aliases` dictionary. Unfortunately, print and pdb doesn't work inside the function and I don't know how to test this change or write test cases for the same.

Any pointers will be highly helpful.

Thanks