For Postdoc positions seeking experts in programming language, what are the expectations and what should my strategy be suitable for those positions?
It was just using an available inbuilt function and wrapping a program around it to serve my purpose.


To be honest, this sounds like the majority of programming that takes place in academia.

Obviously the exact skill requirements will be different for every position, so I can't give you any specific advice, but knowing how to link together existing functions in order to create a program that you want is a useful skill that not everyone has. Don't let your impostor syndrome get the better of you.

Your advisor or someone else in your particular field might be able to offer advice on what skills you should focus on developing.

Background: I recently finished an MA in a field where many researchers are using programming, but also many are not. I have a programming background, but many students with much less programming experience than I have were able to be successful in writing programs for their research.