Can you please explain this piece of code?

Hi Panagiotis!

Thanks for reaching out.

The given sample represents a list comprehension in Python, which is a concise method for generating lists. It loops over products_on_sale, sale_prices, and quantities, multiplying the price and quantity together, and printing the chair_type along with the computed product for each combination of chair_type, price, and quantity.

filter() is a built-in function in Python that constructs an iterator from elements of an iterable for which a function returns true. The typical usage is filter(function, iterable), where function tests the truthiness of each element. 

Hope this helps.

Best,

Ivan