Nice work! We have learned about all sorts of advanced containers which can help make programming easier, more organized, and more optimized! We even learned how to make our own advanced containers using container wrappers. Let’s review the use case for each of the advanced containers from the collections class:
deque- An advanced container which is optimized for appending and popping items from the front and back. For accessing many elements positioned elsewhere, it is better to use a
list.
- An advanced container which is optimized for appending and popping items from the front and back. For accessing many elements positioned elsewhere, it is better to use a
namedtuple- The
namedtuplelets us create an immutable data structure similar to atuple, but we don’t have to access the stored data using indices. Instead, we can create instances of ournamedtuplewith named attributes. We can then use the.operator to retrieve data by the attribute names.
- The
Counter- This advanced container automatically counts the data within a hashable object which we pass into it’s constructor. It stores it as a dictionary where the keys are the elements and the values are the number of occurrences.
defaultdict- An advanced container which behaves like a regular dictionary, except that it does not throw an error when trying to access a key which does not exist. Instead, it creates a new
key:valuepair where the value defaults to what we provide in the constrictor for thedefaultdict.
- An advanced container which behaves like a regular dictionary, except that it does not throw an error when trying to access a key which does not exist. Instead, it creates a new
OrderedDict- The
OrderedDictcombines the functionality of alistand adictby preserving the order of elements, but also allowing us to access values using keys without having to provide an index for the position of stored dictionaries.
- The
ChainMap- This interesting container combines multiple mappings into a single container. When accessing a value using a key, it will search through every mapping contained within until a match is found or the end is reached. It also provides some useful methods for grouping parent and child mappings.
UserDict- This is a container wrapper which lets us create our own version of a dictionary
UserList- This is a container wrapper which lets us create our own version of a list
UserString- This is a container wrapper which lets us create our own version of a string
Let’s try combining some of these concepts by adding one last addition to our clothes store app!
Instructions
The final addition to our clothes store app will be some logic for bundling overstocked items into groups to sell at once. We would like to split our items by price and then pick three cheaper items and two more expensive items per bundle. Finally, we are going to promote the bundles which have a value greater than 100 dollars.
For the first step, import the deque and namedtuple classes from the collections module and create a new deque called split_prices.
Now that the deque has been created, for every clothes item in the overstock_items list, if the price if greater than 20 dollars than append the item to the front of split_prices, otherwise append it to the back of split_prices.
To make the data easier to read and work with, create a namedtuple subclass called ClothesBundle. Set the typename to ClothesBundle and the field_names to bundle_items and bundle_price.
This next step is a bit tricky. First, create an empty list called bundles. Use a loop to continue iterating as long as there are at least 5 elements left in split_prices.
On each iteration, append a new ClothesBundle object to the bundles list. The ClothesBundle object will be created by making a bundle of three cheap items and two expensive items. This can be accomplished using list of items by popping from the back of split_prices three times and the popping from the front of split_prices two times.
Use that list of clothes items as the bundle_items in theClothesBundle. Calculate the sum of the prices for the bundle and store that as the bundle_price in the ClothesBundle.
Use the bundles list to find out which bundles should be promoted. Create a new list called promoted_bundles. For every bundle in bundles which has a total value of over 100 dollars, add that bundle to promoted_bundles.
Finally, print out the list of promoted_bundles to see the result!