How to access a value in a dictionary which is inside a list and modify one value?

Question

I'm trying to iterate a list of dictionaries with a for loop in this way:

my_list = []

while True:
    print("Welcome, choose number 1")
    print("1.- Coke")
    numb = input()

    if numb is "1":
        for l in my_list:
            if l["product"] is "coke":
                l["count"] += 1 
            else:
                Coke = {"product":"coke", "count":1, "price":17.5}
                my_list.append(Coke)

What I expect the code to do is to search in each dictionary inside the list to find a match and add 1 to count value or in case such dictionary don't exist to create it and append it, but when running the code it just keeps my_list empty.

I've tried to delete the iteration and go directly to the creation of the dict which it does without a problem, but when doing the iteration I got no result.

Answer 1

使用 list_name[list_index][dict_key] 访问字典列表中字典中的值，前提是列表索引和字典键已知

Answer 2

The problem with your code is

Initially, my_list is empty so the for loop is not executing at all.So your final result will be always an empty list. Try including a single element in the my_list

my_list = [{"product":"coke", "count":1, "price":17.5}]

while True:
    print("Welcome, choose number 1")
    print("1.- Coke")
    numb = input()

    if numb is "1":
        for l in my_list:
            if l["product"] is "coke":
                l["count"] += 1 
            else:
                Coke = {"product":"coke", "count":1, "price":17.5}
                my_list.append(Coke)

Try this will solve your problem.

Answer 3

First of all, in Python we use == to compare with a literal, and if you use is , Python will give a SyntaxWarning . Second, in your code, if my_list is empty, then the code after for l in my_list won't be executed because it won't iterate over anything. So the code can be:

my_list = []

while True:
    print("Welcome, choose number 1")
    print("1.- Coke")
    numb = input()

    if numb == "1":
        for l in my_list:
            if l["product"] == "coke":
                l["count"] += 1
                break
        else:
            Coke = {"product": "coke", "count": 1, "price": 17.5}
            my_list.append(Coke)

Where the else after the for means "if the for exited without a break ".
Hope it helps you ;-)