FAQ: Collections - UserDict

This community-built FAQ covers the “UserDict” exercise from the lesson “Collections”.

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Learn Intermediate Python 3

FAQs on the exercise UserDict

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What are the benefits of using UserDict as a parent class of a custom data structure compared to using dict as a parent class of a custom data structure? What are the benefits of using dict as a parent class of a custom data structure compared to using Userdict as a parent class of a custom data structure?

I’m a little confused by the solution - where is refers to self.data,items() - where does the actual data part come from?
is that because data is fed into the class initiation and if so doesn’t it make this particular class quite fragile as not all dictionaries would be called data so not sure it’s coded very robustly (if I’ve understood the intent correctly).

I think I get it now, there is a data property in the parent UserDict class I didn’t have visibility of, I have to lookup the details on Python.org to better understand that on.

I had overlooked the item in the description that explained this:
" This class contains all of the functionality of a normal dict , except that we can access the dictionary data through the data property."

3 Likes

Dear all,

Why do I get a “type error: string indices must be integers” when using the code block below?
My reasoning is that we first iterate through each Order and then access each Orders dictionary with the key “order_status”…

data = {'order_4829': {'type': 't-shirt', 'size': 'large', 'price': 9.99, 'order_status': 'processing'}, 'order_6184': {'type': 'pants', 'size': 'medium', 'price': 14.99, 'order_status': 'complete'}, 'order_2905': {'type': 'shoes', 'size': 12, 'price': 22.50, 'order_status': 'complete'}, 'order_7378': {'type': 'jacket', 'size': 'large', 'price': 24.99, 'order_status': 'processing'}} # Write your code below! from collections import UserDict class OrderProcessingDict(UserDict): def clean_orders(self): del_items = [] for order in self.data: if order["order_status"] == "complete": del_items.append(order) for order in del_items: del self.data[order] process_dict = OrderProcessingDict(data) process_dict.clean_orders()

I see a problem in the loop
order is a string (each key)
so to access the value at that dictionary, you would use self.data[order]

So
if order["order_status"] == "complete":
should be
if self.data[order]["order_status"] == "complete":