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README.md

Practical 07 - Classes 2

Remember to do your work for this prac (as is usual now) in a new branch, then do a pull request, mentioning the correct student to get a code review.
Remember to check and do your code review when requested.

Find the right student to mention here (this is the same file/link every prac)

You do not need to wait to receive your code review before starting.
If you have not received a review, you can still complete this process. The PR URL is still the same and the reviewer can still review the code even though it has been merged.

Let's run through the process again:

  • Merge your PR on GitHub.
    This updates your remote master branch to contain the work from your last feedback branch.
  • In PyCharm, Checkout your local master branch.
  • Pull to update your local master branch. This pulls in the changes from GitHub including the merge.
  • (Double-check that you are on the master branch, not the feedback branch.)
  • Create a new branch, prac_07_feedback.
  • Do your prac work.

README

As you have seen, a "README" file is a common aspect of a software project.
A good README usually introduces a project, provides details about the author, and includes any instructions needed for someone else to benefit from your project.
We will now add a README to our practicals repository.

New > File README.md (exact spelling) in your practicals main/root directory (not in prac_07 or similar).
If you already have one, just edit it. You don't need to create a new one.
PyCharm knows about markdown files, so it will give you syntax highlighting and other features as you type.

Include at least the following in your practicals README:

  • Headings 1 and 2. These lines will start with # and ## respectively. Use headings appropriately and semantically.
  • Brief information about the repo and yourself.
  • A list (markdown -) of at least 3 main lessons you have learned about "clean code" in this subject.
  • Proper links (linked names, not 'bare URLs') to the Programming Patterns page and the CP1404 Practicals instructions repo.

Here's the official Markdown syntax guide to help you learn how to do lists, links, etc.

Please take this task seriously. Good developers care about documentation, following conventions, correctly-formatted code, user experience... "Reformat Code" to ensure your formatting is correct before you finish and commit your README.
After you've committed, review your README on GitHub and check that it looks good. If it doesn't, fix it and update it.

Walkthrough Example

This example program loads a number of "Programming Languages" from a file and saves them in objects using the class we wrote recently.

Download 3 files from this folder. For now let's start with:

Read the comments and the code in language_file_reader.py to see how it works.

Notice how:

  • the file is opened and closed
  • readline() is used to read (only) the first line, which just ignores the header in the CSV file
  • a for loop is used to read the rest of the file
  • reflection is stored in the file as a string, but this client code converts it to a Boolean ready for the class. It's not the class's job to do this conversion but the client's.
  • There are also a few other versions included that use Python's csv module and a namedtuple. Read through to see how they work!

Modifications

  1. Add another language to the file - and make sure it still works properly.
  2. Add another field to your ProgrammingLanguage class for Pointer Arithmetic. This will be a Boolean variable.
    This work may take a bit of effort, as you need to update the class and any code that uses it. You also need to add the appropriate values to your data file (in a form like reflection).
  3. Check that your code is complete including updating any docstrings.
    Are __str__ and other methods complete and good?
  4. Run the language_file_reader.py program again to test that it works correctly with your modified ProgrammingLanguage class. Change this client code as needed so that it works.

Languages that support pointer arithmetic include C, C++, C# and D.
Go, Rust and Swift have pointers but no pointer arithmetic.
Many languages, including Python, Visual Basic, Java and JavaScript, do not (really) have pointers, so they do not have pointer arithmetic.

Intermediate Exercises

More Guitars!

File: guitar.py
File: myguitars.py

Start by copying guitar.py from your prac_06 folder into this week's prac.
We could import it, but we want to modify it, so we'll leave the old one unchanged.

Save the file: guitars.csv to your prac folder.
This file contains lines like:

Fender Stratocaster,2014,765.4

So, the format/protocol is:

Name,Year,Cost

Write a program to read all of these guitars and store them in a list of Guitar objects, using the class that you wrote recently.
Display these using a loop.
Use a main and other appropriate functions.

Now sort the list by year (oldest to newest) and display them in sorted order...
How do you do that?
Sorting requires that Python knows how to compare objects...
If we just use:

guitars.sort()

We get an error like:

TypeError: unorderable types: Guitar() < Guitar()

So we need to define how the < operator should work.
Do you remember how?

Write code for the __lt__ (less than) method so that it compares Guitars by year.
Then test and see if it sorts correctly now.

Commit as you go

This is a good time for a commit. You haven't completed the whole task, but you've reached a "small milestone".
Commit with an appropriate message using a capital and the imperative mood before moving on.
You might write something like:

Complete first part of More Guitars exercise

Now add to your program to ask the user to enter their new guitars (just like your program from an earlier prac).
Store these new guitars in your list of guitar objects, then
write all of your guitars to the data file guitars.csv.

Test that this worked by opening the data file, and also by running the program again to make sure it reads the new guitars.

At this stage, you should have a reasonable quantity of code.
If you have not yet implemented separate functions for separate tasks, then refactor your code to use functions appropriately.

Do-from-scratch Exercises

Project Management Program

File: project.py
File: project_management.py

Read the instructions, then enter a time estimate in your module docstring.

The instructions for this exercise are intentionally not step-by-step.
We want you to use what you've learned about good program and class design, iterative development, version control, clean code, etc. to determine the best approach.

Save the projects.txt data file to your prac folder.
This file contains the data for this exercise delimited by tabs.
The first line is a header, explaining the fields for each project.

Write a program in project_management.py to load and save a data file and use a list of Project objects.

Load projects from the default data file, projects.txt, when the program starts, before the menu.
When the user quits, give them the choice of saving to the default file.
Note that there are menu options for loading from and saving to different files.

Your program should contain a menu with the following options:

  • Load projects
    (Prompt the user for a filename to load projects from and load them)
  • Save projects
    (Prompt the user for a filename to save projects to and save them)
  • Display projects
    (Display two groups: incomplete projects; completed projects, both sorted by priority)
  • Filter projects by date
    (Ask the user for a date and display only projects that start after that date, sorted by date)
  • Add new project
    (Ask the user for the inputs and add a new project to memory)
  • Update project
    (Choose a project, then modify the completion % and/or priority - the user can leave either input blank to retain existing values)

Note

You should notice that there are two different scenarios for both loading and saving.
Consider SRP and how you can write a single function for loading that you use in both scenarios: the default filename and the user-selected filename.

Expectations:

  • Commit your work as you go (iterative development).
  • Some of this could be considered relatively "hard" - do the easy bits first, then add more as you go.
  • Use the datetime module for the project start date.
  • Write your class such that you are able to sort/compare Project objects based on priority order.
  • Use at least one utility/helper method in your class.
    Think of our examples like is_vintage for Guitar and what you might use for a Project.
  • Follow good design principles like SRP and DRY. Notice that there's two kinds of loading, so write one function to handle both. Same for saving.
  • Write good clean code (no pylint warnings) with good naming and design (as always!)

Here are two suggestions to leave until last (iterative development):

  • Error checking. Do no error checking to start with.
  • Date formatting. Just use a string until most everything else works, then, here are some suggestions.

Note

Remember how in our walkthrough above, we saw that it is not the class's job to convert the file's "Yes" string into the Boolean True for the class? That's the job of the client code.
Here, when you create a Project object, you will want to convert the date string to a datetime object, but it's not the class's job - it's the client code's job.

The following code reads a string from user input, converts it to a date object (using the strptime method from the datetime type), prints the day of the week (%A) and then prints the date as a string:

import datetime

date_string = input("Date (d/m/yyyy): ")  # e.g., "30/9/2022"
date = datetime.datetime.strptime(date_string, "%d/%m/%Y").date()
print(f"That day is/was {date.strftime('%A')}")
print(date.strftime("%d/%m/%Y"))

Remember to enter your actual time in your module docstring.
Are you getting better at estimating?

Is this exercise too big? Will it take too long? Probably.
Not every student can do every task in every subject. Some things are challenging and that's OK.

Be systematic, thoughtful, use the patterns you've learned, copy from previous examples... be efficient.
Don't waste time reinventing new/different ways to do "standard" things like menus. Follow the patterns.

Sample output

Welcome to Pythonic Project Management
Loaded 5 projects from projects.txt
- (L)oad projects  
- (S)ave projects  
- (D)isplay projects  
- (F)ilter projects by date
- (A)dd new project  
- (U)pdate project
- (Q)uit
>>> d
Incomplete projects: 
  Organise Pantry, start: 20/07/2022, priority 1, estimate: $25.00, completion: 55%
  Build Car Park, start: 12/09/2021, priority 2, estimate: $600000.00, completion: 95%
  Mow Lawn, start: 31/10/2022, priority 3, estimate: $3.00, completion: 0%
  Record Music Video, start: 01/12/2022, priority 9, estimate: $250000.00, completion: 0%
Completed projects: 
  Read 7 Habits Book, start: 13/12/2021, priority 6, estimate: $99.00, completion: 100%
- (L)oad projects  
- (S)ave projects  
- (D)isplay projects  
- (F)ilter projects by date
- (A)dd new project  
- (U)pdate project
- (Q)uit
>>> u
0 Build Car Park, start: 12/09/2021, priority 2, estimate: $600000.00, completion: 95%
1 Mow Lawn, start: 31/10/2022, priority 3, estimate: $3.00, completion: 0%
2 Organise Pantry, start: 20/07/2022, priority 1, estimate: $25.00, completion: 55%
3 Record Music Video, start: 01/12/2022, priority 9, estimate: $250000.00, completion: 0%
4 Read 7 Habits Book, start: 13/12/2021, priority 6, estimate: $99.00, completion: 100%
Project choice: 3
Record Music Video, start: 01/12/2022, priority 9, estimate: $250000.00, completion: 0%
New Percentage: 20
New Priority: 
- (L)oad projects  
- (S)ave projects  
- (D)isplay projects  
- (F)ilter projects by date
- (A)dd new project  
- (U)pdate project
- (Q)uit
>>> a
Let's add a new project
Name: Practical 7
Start date (dd/mm/yy): 1/11/2022
Priority: 1
Cost estimate: $0
Percent complete: 32
- (L)oad projects  
- (S)ave projects  
- (D)isplay projects  
- (F)ilter projects by date
- (A)dd new project  
- (U)pdate project
- (Q)uit
>>> f
Show projects that start after date (dd/mm/yy): 20/7/2022
Organise Pantry, start: 20/07/2022, priority 1, estimate: $25.00, completion: 55%
Mow Lawn, start: 31/10/2022, priority 3, estimate: $3.00, completion: 0%
Practical 7, start: 01/11/2022, priority 1, estimate: $0.00, completion: 32%
Record Music Video, start: 01/12/2022, priority 9, estimate: $250000.00, completion: 20%
- (L)oad projects  
- (S)ave projects  
- (D)isplay projects  
- (F)ilter projects by date
- (A)dd new project  
- (U)pdate project
- (Q)uit
>>> u
0 Build Car Park, start: 12/09/2021, priority 2, estimate: $600000.00, completion: 95%
1 Mow Lawn, start: 31/10/2022, priority 3, estimate: $3.00, completion: 0%
2 Organise Pantry, start: 20/07/2022, priority 1, estimate: $25.00, completion: 55%
3 Record Music Video, start: 01/12/2022, priority 9, estimate: $250000.00, completion: 20%
4 Read 7 Habits Book, start: 13/12/2021, priority 6, estimate: $99.00, completion: 100%
5 Practical 7, start: 01/11/2022, priority 1, estimate: $0.00, completion: 32%
Project choice: 0
Build Car Park, start: 12/09/2021, priority 2, estimate: $600000.00, completion: 95%
New Percentage: 100
New Priority: 3
- (L)oad projects  
- (S)ave projects  
- (D)isplay projects  
- (F)ilter projects by date
- (A)dd new project  
- (U)pdate project
- (Q)uit
>>> d
Incomplete projects: 
  Organise Pantry, start: 20/07/2022, priority 1, estimate: $25.00, completion: 55%
  Practical 7, start: 01/11/2022, priority 1, estimate: $0.00, completion: 32%
  Mow Lawn, start: 31/10/2022, priority 3, estimate: $3.00, completion: 0%
  Record Music Video, start: 01/12/2022, priority 9, estimate: $250000.00, completion: 20%
Completed projects: 
  Build Car Park, start: 12/09/2021, priority 3, estimate: $600000.00, completion: 100%
  Read 7 Habits Book, start: 13/12/2021, priority 6, estimate: $99.00, completion: 100%
- (L)oad projects  
- (S)ave projects  
- (D)isplay projects  
- (F)ilter projects by date
- (A)dd new project  
- (U)pdate project
- (Q)uit
>>> q
Would you like to save to projects.txt? no, I think not.
Thank you for using custom-built project management software.

Ready for Kivy?

Next week, we will be writing and running programs with the Kivy GUI toolkit.

Please test you can successfully run this test code.

If you cannot run the above code, please complete the setup this week:
Follow these instructions

Practice & Extension Work

How did you go with this section from the last prac?
If you didn't complete all of that work, then go back and work on those exercises.

Extension

"Pickling is the process whereby a Python object hierarchy is converted into a byte stream, and “unpickling” is the inverse operation, whereby a byte stream (from a binary file or bytes-like object) is converted back into an object hierarchy."

You can use Python's pickle module to load and save data from files without having to manually process data.
You essentially just "save" your variables in memory to a file.

Study the provided pickling demo to see how to use pickling and JSON to load and dump objects to and from memory.

Now, write a new version of the Project Management Program to use pickling to load and save the data.

Summary

  • README.md (This is the main README you did in this prac, not the nearly-empty prac_07/README)
  • language_file_reader.py, programming_language.py, languages.csv
  • guitar.py, myguitars.py
  • project.py, project_management.py