here you can do it using extending/patching javascript (it's big hack)  there is no option from python side
DO NOT IMPLEMENT it unless it's absolutely necessary. 

Share your use case so community can help you.

Save record on button click if record not saved is a very early design decision and completely fundamental mechanism of how odoo works. there is pretty good reasoning behind it
ref: https://github.com/odoo/odoo/issues/20942#issuecomment-344934525​

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