Filter with a Query String

A client often wants only part of the data, and it can say so in the URL. Everything after the ? is the query string, made of name=value pairs. In /products?max_price=10 the path is still /products, so the same route answers: max_price is the name and 10 is the value.

In Flask you read a query parameter with request.args.get. Everything in a URL is text, so add type=int when you want a whole number. When the parameter is missing, or isn't a whole number, you get None. Here is the idea on another route:

@app.get("/double")
def double():
    number = request.args.get("number", type=int)
    if number is None:
        return "Send a whole number, like /double?number=4"
    return str(number * 2)

The filter is a loop you already know: start an empty list, go through the products, and append the ones that pass the check. When there is no max_price, every product passes, so /products still answers the whole list. Your code must give:

GET /products?max_price=10     →  200  [{"id": 2, "name": "Notebook", …}, {"id": 4, "name": "Pen", …}]
GET /products?max_price=12     →  200  [{"id": 1, "name": "Mug", …}, {"id": 2, …}, {"id": 4, …}]
GET /products?max_price=1      →  200  []
GET /products                  →  200  all 4 products
GET /products?max_price=cheap  →  200  all 4 products
GET /products/3                →  200  {"id": 3, "name": "Lamp", "price": 29, "category": "home"}

Your task: change get_products so it reads max_price from the query string and answers only the products that cost max_price or less, or every product when there is no limit.

Assignment
Follow the Coding Tutorial to read max_price and filter the list in get_products.

Hint
Check max_price is None first, then or, then compare the price with <=. Return result after the loop, not inside it.