Swap Meet

Skills Assessed

• Following directions and reading comprehension
• Reading tests
• Creating classes
  • Classes have attributes and instance methods
• Importing modules
• Working with attributes that are lists of instances
• Implementing instance methods that interact with other instances and objects
• Implementing inheritance
• Overriding methods from superclasses and Object

Goal

You want to organize a swap meet! You have a bunch of stuff. So do your friends! It would be awesome if each person could swap one of their things with another person's things.

For this event, you want each person to register online as a vendor. Also, they should list an inventory list of things.

You envision an app where vendors can swap items between different inventories. But what would that backend logic look like?

For this project, given some features that the vendors want, create a set of classes, following the directions below. The directions will lead you to create many class definitions, their attributes and instance methods, and some other cool features. Vendors will be able to swap their top item and swap items by category!

One-Time Project Setup

Follow these directions once, at the beginning of your project:

1. Navigate to your projects folder named projects

$ cd ~/Developer/projects

2. "Clone" (download a copy of this project) into your projects folder. This command makes a new folder called swap-meet, and then puts the project into this new folder.

$ git clone ...

Use ls to confirm there's a new project folder

3. Move your location into this project folder

$ cd swap-meet

4. Create a virtual environment named venv for this project:

$ python3 -m venv venv

5. Activate this environment:

$ source venv/bin/activate

Verify that you're in a python3 virtual environment by running:

• $ python --version should output a Python 3 version
• $ pip --version should output that it is working with Python 3

6. Install dependencies once at the beginning of this project with

# Must be in activated virtual environment
$ pip install -r requirements.txt

Summary of one-time project setup:

• cd into your projects folder
• Clone the project onto your machine
• cd into the swap-meet folder
• Create the virtual environment venv
• Activate the virtual environment venv
• Install the dependencies with pip

Project Development Workflow

1. When you want to begin work on this project, ensure that your virtual environment is activated:

$ source venv/bin/activate

2. Find the test file that contains the test you want to run.

   • Check the tests folder, and find the test file you want to run
   • In that test file, read through each test case

3. Run the tests for your specific wave

# Must be in activated virtual environment
$ pytest tests/test_wave_01.py

4. Focus on the top test failure. Read through the test failure, and understand why the failure is happening. Confirm your findings with a classmate.

5. Make a plan to fix the test failure.

6. Write code to fix the test failure.

7. Re-run the tests.

8. Repeat steps 5-7 until that test passes!

9. Repeats steps 4-8 until you have finished all tests in the file.

10. Begin using the test file of the next wave!

11. When you are finished working for the day, deactivate your environment with deactivate or closing the Terminal tab/window

$ deactivate

Details About How to Run Tests

Run all tests that exist in this project with:

# Must be in activated virtual environment
$ pytest

If you want to run all tests that exist in one file, use:

# Must be in activated virtual environment
$ pytest tests/test_file_name.py

... where test_file_name.py is replaced with the correct test file name.

If you want to see any print statements print to the console, add -s to the end of any pytest command:

# Must be in activated virtual environment
$ pytest -s

Project Write-Up: How to Complete and Submit

The goal of this project is to write code in various files in the swap_meet directory so that as many of the tests pass as possible.

To complete this project, use the above workflow and follow these steps:

1. Start with making the tests in test_wave_01.py pass.
2. Review your code in the swap_meet directory and see if there are ways you can make the code more readable.
3. Then, work on making the tests in test_wave_02.py pass.
4. Review your code in the swap_meet directory
5. Repeat on all test files until submission time.

At submission time, no matter where you are, submit the project via Learn.

Project Directions

This project is designed such that one could puzzle together how to implement this project without many directions. Being able to use tests to drive project completion is a skill that needs to be developed; programmers often take years to develop this skill competently.

When our test failures leave us confused and stuck, let's use the detailed project requirements below.

Wave 1

The first two tests in wave 1 imply:

• There is a module (file) named vendor.py inside of the swap_meet package (folder)
• Inside this module, there is a class named Vendor
• Each Vendor will have an attribute named inventory, which is an empty list by default
• When we create initialize an instance of Vendor, we can optionally pass in a list with the keyword argument inventory

The remaining tests in wave 1 imply:

• Every instance of Vendor has an instance method named add, which takes in one item

• This method adds the item to the inventory

• This method returns the item that was added

• Similarly, every instance of Vendor has an instance method named remove, which takes in one item

• This method removes the matching item from the inventory

• This method returns the item that was removed

• If there is no matching item in the inventory, the method should return False

Wave 2

The first tests in wave 2 imply:

• There is a module (file) named item.py inside of the swap_meet package (folder)

• Inside this module, there is a class named Item

• Each Item will have an attribute named category, which is an empty string by default

• When we initialize an instance of Item, we can optionally pass in a string with the keyword argument category

• Instances of Vendor have an instance method named get_by_category

  • It takes one argument: a string, representing a category
  • This method returns a list of Items in the inventory with that category

Wave 3

The first test in wave 3 implies:

• When we stringify (convert to a string) an instance of Item using str(), it returns "Hello World!"
  • This implies Item overrides its stringify method. We may need to research the __str__ method for more details!

The remaining tests in wave 3 imply:

• Instances of Vendor have an instance method named swap_items
  • It takes 3 arguments:
    1. an instance of another Vendor, representing the friend that the vendor is swapping with
    2. an instance of an Item (my_item), representing the item this Vendor instance plans to give
    3. an instance of an Item (their_item), representing the item the friend Vendor plans to give
  • It removes the my_item from this Vendor's inventory, and adds it to the friend's inventory
  • It removes the their_item from the other Vendor's inventory, and adds it to this Vendor's inventory
  • It returns True
  • If this Vendor's inventory doesn't contain my_item or the friend's inventory doesn't contain their_item, the method returns False

Wave 4

The tests in wave 4 imply:

• Instances of Vendor have an instance method named swap_first_item
  • It takes one argument: an instance of another Vendor, representing the friend that the vendor is swapping with
  • This method considers the first item in the instance's inventory, and the first item in the friend's inventory
  • It removes the first item from its inventory, and adds the friend's first item
  • It removes the first item from the friend's inventory, and adds the instances first item
  • It returns True
  • If either itself or the friend have an empty inventory, the method returns False

Wave 5

The tests in Wave 5 imply there are three additional modules with three additional classes:

• Clothing

  • Has an attribute category that is "Clothing"
  • Its stringify method returns "The finest clothing you could wear."

• Decor

  • Has an attribute category that is "Decor"
  • Its stringify method returns "Something to decorate your space."

• Electronics

  • Has an attribute category that is "Electronics"
  • Its stringify method returns "A gadget full of buttons and secrets."

• All three classes and the Item class have an attribute called condition, which can be optionally provided in the initializer. The default value should be 0.

• All three classes and the Item class have an instance method named condition_description, which should describe the condition in words based on the value, assuming they all range from 0 to 5. These can be basic descriptions (eg. 'mint', 'heavily used') but feel free to have fun with these (e.g. 'You probably want a glove for this one..."). The one requirement is that the condition_description for all three classes above have the same behavior.

Using Inheritance

Now, we may notice that these three classes hold the same types of state and have the same general behavior as Item. That makes this is a great opportunity to use inheritance! If you haven't already, go back and implement the Clothing, Decor, and Electronics classes so that they inherit from the Item class. This should eliminate repetition in your code and greatly reduce the total number of lines code in your program!

Hint: Importing Item

You'll need to refer to Item in order to declare it as a parent. To reference the Item class from these modules, try this import line:

from swap_meet.item import Item

Wave 6

The first three tests in wave 6 imply:

• Vendors have a method named get_best_by_category, which will get the item with the best condition in a certain category
  • It takes one argument: a string that represents a category
  • This method looks through the instance's inventory for the item with the highest condition and matching category
    • It returns this item
    • If there are no items in the inventory that match the category, it returns None
    • It returns a single item even if there are duplicates (two or more of the same item with the same condition)

The remaining tests in wave 6 imply:

• Vendors have a method named swap_best_by_category, which will swap the best item of certain categories with another Vendor
  • It takes in three arguments
    • other, which represents another Vendor instance to trade with
    • my_priority, which represents a category that the Vendor wants to receive
    • their_priority, which represents a category that other wants to receive
  • The best item in my inventory that matches their_priority category is swapped with the best item in other's inventory that matches my_priority
    • It returns True
    • If the Vendor has no item that matches their_priority category, swapping does not happen, and it returns False
    • If other has no item that matches my_priority category, swapping does not happen, and it returns False

DRYing up the code

To further reduce the amount of repeated code in your project, consider how swap_best_by_category and swap_first_item might be able to make use of swap_items. Is there a way that these methods could incorporate a call to swap_items into the body of these methods?

Try it out and see if the tests still pass! If you can't get them to pass with this refactor, you can always return to the most recent working commit before you submit the project!

Optional Enhancements

Should a project be completed before submission, and there is a desire for optional enhancements, consider this idea:

• Items have age
  • Add an age attribute to all Items
  • Implement a Vendor method named swap_by_newest, using any logic that seems appropriate