Update Individual_file_extraction.py

[YeabinMoonEcon]

I am not sure how I follow even in this repository. There are some problems across the codes. They are minor, so please update them all.

1. In Python, there is generally no problem with importing a module inside a function. It is allowed, and Python will handle it correctly. However, importing a module inside a function can affect performance as the module will be imported each time the function is called. Put them on the top of the code if possible.

2. You need to add comments to your code to provide explanations and make it more understandable to yourself and others who might read it later.

[YeabinMoonEcon]

You don't have to merge this. I just want to show you an example.