prac_01

Practical 01 - Basic Python Programming in PyCharm

Welcome to CP1404 practicals!

If you haven't read the introduction to practicals, please read this now.

PyCharm Project Setup

Let's start by getting you used to working with the PyCharm IDE (Integrated Development Environment).

If you are using your own computer, complete the instructions for setting up all the required software at: https://github.com/CP1404/Starter/wiki/Software-Setup
To start with, you don't need Git or Kivy, just Python 3 and PyCharm.

Note

Your version of PyCharm may look different from our images and instructions below, but hopefully they are close enough for you to follow.

A PyCharm project is a folder on the computer that contains Python source code files and related resource files to make your program run... but it's more than that.
Always do your coding in files that are part of a project - NOT just individual files you open.

For this week, we will just make a project called prac_01 and work on a few files.
Next week, we will learn to use version control with Git, and we will make a new project for your practicals.

1. Run PyCharm.
   You should see a window with a link to create a new project.

2. Click on Create New Project (not notebook) and choose Pure Python.
   PyCharm lets you choose where to store your new project and what interpreter to use.

   • the location can be changed to any place you have access to. Use a folder that you will be able to find later

   • the interpreter is the version of Python used to run our code.
     Select "Custom environment" and "Select existing" for Python 3.

   

3. Next, let's add our first source code file to the project.
   Right-click on the project name and select
   New > Python File
   

4. Enter the name hello.py. Always give your files descriptive names that are easy to understand.

5. PyCharm created a new source code file in the project folder and opened the editor window. Look at the interface and see what information you can identify: row/column, syntax errors, Python version...

6. Let's learn our first shortcut! Press Shift+Enter to add a blank line below the one you're on (no matter where the cursor is). Nice!
   Do it again, then add the famous line:

   print("Hello world")

7. To run this standard first program, right-click in the code editor window and select the run option.
   If it didn't work, please check for what the problem might be, then if you need to, ask the nearest person for help.

   

Temperatures

In the next example, we will write a program that can convert between Celsius and Fahrenheit temperatures.

1. Right-click on your project folder and create a new Python file here called temperatures.py
   To copy the starter code for this program, click on the file link below, then click the Raw button in GitHub to get a version suitable for copying. Don't just copy from the normal view without clicking Raw, or you will not get proper formatting. OK?
   Download or copy temperatures.py

2. Run this program by right-clicking in the code window and choosing run. Try converting a couple of Celsius values to Fahrenheit.

3. Now complete the TODO. Replace pass with your code to do the opposite temperature conversion (F to C). Test your code.

Productivity Tips & PyCharm Configuration

Good programmers (that's you!) don't waste time.
Here are some important tips and settings to be efficient...

• As you are typing code, notice PyCharm's suggestions and highlights.

• As you type in the name of an existing identifier, PyCharm will show you a list of matching names that you can select from by simply pressing ENTER.
  Don't use your mouse to click on these. Shortcuts aren't shortcuts if you use them the long way!

• The more you type in, the more specific the list becomes
  

• Notice also that PyCharm colours different parts of the code to help you understand what they are - variables, literals, comments, etc.

• You may also notice that the # TODO comment is special. PyCharm knows you want to come back to this. You can list all of your TODOs in a project, and it can warn you of unfinished or new TODOs when you commit your work to version control.

• If you see an underline, move your mouse over it (but don't click!) to see what the issue is, and look at the action PyCharm suggests to fix it for you. Example:
  

• Please make use of PyCharm's useful support features so that you can work better and faster. It's not cheating; it's good practice!

If you don't see underlines for formatting warnings, change the following setting:
File (or PyCharm on Mac) > Settings > Editor > Inspections
Search for "PEP" and select "PEP 8 Coding Style Violation" then change the severity to "Weak Warning" as in this screenshot:

Warning

We love being productive, and we don't want you to waste time, BUT...
We're not just trying to get through this work as quickly as possible. What we really want is to learn.
With this in mind, we are purposely choosing NOT to use AI in this subject at all.
So, turn off PyCharm's very handy AI full line completion now.

Open the settings:
File (or PyCharm on Mac) > Settings > Editor > General > Inline Completion
Untick "Enable local Full Line completion suggestions"

Here's a quick story to help illustrate the point.

Lindsay was working with a student in a prac recently whose code had some problems.
He asked the student why they had chosen to implement the code that way, and the student replied:
"Not gonna lie, I just pressed Tab multiple times."

• If you want to finish the job quickly, get AI to do it... but you will not learn much.
• If you want to learn and build your own skills, don't use AI... but choose to learn all you can.

While we're thinking about being more productive...
A good way to organise your workspace is to put these instructions on one side of your screen, and your code (PyCharm) on the other side. Windows users can use the Windows key + arrow shortcuts for this.
Now you don't have to waste time switching back and forth between these two windows!
Drag the bar between your project files and your code so that you can see lots of code (or hide the project window altogether with Alt+1).

Got PyCharm configured and your windows organised? Let's keep going...

Intermediate Exercises

Okay, let's practise using PyCharm to write simple programs.

1. Sales Bonus

File: sales_bonus.py

Create a new Python file called sales_bonus.py, and copy the following docstring at the top of the file. A docstring is a triple-quoted special comment "doc(umentation) string".

"""
Program to calculate and display a user's bonus based on sales.  
If sales are under $1,000, the user gets a 10% bonus.  
If sales are $1,000 or over, the bonus is 15%.  
"""

Now write the Python code to complete the program according to that docstring.
The first line might look like:

sales = float(input("Enter sales: $"))

Run and test the code with a few different values to verify that it works.
Whenever you are testing code, don't just use random values but values that you know the expected output for and that test all paths of execution, including the boundary or edge cases.
So, for this program we could use the following (we're only interested in the values, not the format):

Test Input	Expected Output
500	50
2000	300
1000 (edge case)	150

Please only do the following loop modification when the above part is finished and working.

Now add a loop to this, so that it repeatedly asks for the user's sales and prints the bonus until they enter a negative number.
Be careful with the boundary.
Remember that until is the opposite of while, and if you need help, please check the patterns.
Here's some pseudocode to help you:

get sales
while sales >= 0
    calculate bonus (this line is intentionally incomplete pseudocode)
    print bonus
    get sales
do next thing

2. Debugging:

File: broken_score.py

Someone was trying to write a program to tell the user if their score is invalid, bad, passable or excellent, but their code doesn't work.

Rewrite the following program using the most efficient if, elif, else structure you can. The code is available here at: broken_score.py
Remember to click Raw before copying and pasting so that you get proper formatting!

The intention is that the score must be between 0 and 100 inclusive; 90 or more is excellent; 50 or more is a pass; below 50 is bad. There is no intention to do any repetition.

Be very careful of your boundary conditions... and test systematically.

3. Loops

File: loops.py

Create a file called loops.py and add the following for loop that displays all the odd numbers between
1 and 20 with a space between each one.

for i in range(1, 21, 2):
    print(i, end=' ')
print()

Now write more for loops (using range) to do the following:

Note

We expect to see a complete file with each loop still in it.
Label each of your questions: a, b, c, d

a. count in 10s from 0 to 100: 0 10 20 30 40 50 60 70 80 90 100

b. count down from 20 to 1: 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

c. print a number of stars.
Ask the user for a number, then print that many stars (*), all on one line.

Here's a good time to refer to the Style Guide.
You need a variable to store the "number of stars". As our guide shows, a good name for this is...
number_of_stars.

Note

This is a very simple loop for repeating a number of times.
We use for loops for "definite" iteration like this.
while loops are used for "indefinite" iteration, like error-checking a user input.

Sample output (showing the user input is 4):

Number of stars: 4
****

d. print lines of increasing stars.
Ask the user for a number of lines, then print lines of increasing stars, starting at 1 with no blank line.
E.g., if the user entered 4, your single loop should print:

*
**
***
****

Note

We just asked you to "print n stars/lines". n is a common name for a value like this. As our Style Guide shows, we like readable unambiguous names like number_of_stars and we generally avoid abbreviations.
When there are "world standard" abbreviations like n here, or i for index, we're OK with those.
Since these single-character names have been used in mathematics for hundreds of years, we can safely assume that most readers will understand them.
But this is not licence to use terse names!
Using a for age or x for number of chickens is not OK.
It's not about blindly following arbitrary rules, but about learning what will work well for an appropriate audience.
If in doubt, choose the more descriptive name.

We've now had the walkthrough and the intermediate exercises where you mostly modify and extend existing code, or you have to write something really similar to working code you've been given...
Now we move on to the section where you are given a task to complete with no starting code.
Remember to use the examples above as a guide, and if you're not sure how to do it, go back to the subject teaching. For example, the question below asks for an error-checking loop, which is summarised as one of our standard patterns at: https://github.com/CP1404/Starter/wiki/Programming-Patterns

If you need help, ask a classmate or your tutor.

Do-from-scratch Exercises

Shop Calculator

File: shop_calculator.py

A shop requires a small program that would allow them to quickly work out the total price for a number of items, each with different prices.

The program allows the user to enter the number of items and the price of each different item.
Then the program computes and displays the total price of those items.
If the total price is over $100, then a 10% discount is applied to that total before the amount is displayed on the screen.

Sample output:
The output should look like the sample below, where bold text represents user input.
This uses f-string formatting to set the currency to 2 decimal places.

Note

Whenever we provide sample output, it is a requirement that your solution matches it.

Number of items: 3  
Price of item: 100  
Price of item: 35.56  
Price of item: 3.24  
Total price for 3 items is $124.92  

Create the file shop_calculator.py and write this program.

Note

Start with the main logic, then adjust your program to improve the formatting if you need to.

+ Error checking (input validation loop)

After you have completed the above program...
If the number of items is less than zero, the message "Invalid number of items!" should be displayed and this quantity must be re-entered by the user until it is valid.

Menus

File: menus.py

One very common programming task is to make menus by combining repetition (repeat the program until the user quits) with decision (let the user decide what to do).
The general pattern of a menu-driven program is as follows:

display menu
get choice
while choice != quit option
    if choice == first option
        do first task
    else if choice == <second option>
        do second task
    ...
    else if choice == <n-th option>
        do n-th task
    else
        display invalid input error message
    display menu
    get choice
do final thing, if needed

Warning

A common error when writing menus is to forget to repeat the menu display and prompt at the end (inside) the loop.
Follow the pattern.

Use this pattern to create a very simple menu-driven program according to the pseudocode below:

get name
display menu
get choice
while choice != Q
   if choice == H
       display "hello" name
   else if choice == G
       display "goodbye" name
   else
       display invalid message
   display menu
   get choice
display finished message

Sample output for this program should look like:

Enter name: Guido
(H)ello
(G)oodbye
(Q)uit
>>> A
Invalid choice
(H)ello
(G)oodbye
(Q)uit
>>> H
Hello Guido
(H)ello
(G)oodbye
(Q)uit
>>> G
Goodbye Guido
(H)ello
(G)oodbye
(Q)uit
>>> Q
Finished.

Practice & Extension Work

You will learn better if you spread your work over multiple sessions instead of trying to do all of this in one go.
There are two subsections - practice, with easier questions for you to get more... practice
and extension, with harder questions for you to stretch yourself.

Practice

1. Create an electricity bill estimator, electricity_bill.py
   Inputs should be:

   • price per kWh in cents,
   • daily use in kWh, and
   • number of days in the billing period.

   Example use:

   Electricity bill estimator         
   Enter cents per kWh: 35          
   Enter daily use in kWh: 4.5      
   Enter number of billing days: 90 
   Estimated bill: $141.75            
   

2. (in the same file) Modify your bill estimator by asking the user to choose which tariff they are using - then use the appropriate stored value for cents per kWh.
   Start by defining two constants like below.
   Constants in Python are just variables written in ALL_CAPITALS.

   TARIFF_11 = 0.244618
   TARIFF_31 = 0.136928

   Example use:

   Electricity bill estimator 2.0   
   Which tariff? 11 or 31: 11       
   Enter daily use in kWh: 13.4     
   Enter number of billing days: 90 
   Estimated bill: $295.01         
   

Extension

Menu-driven number sequence generator

sequences.py

A school teacher requires a small program that would allow primary school students to learn about various number sequences. The teacher is interested in a simple menu-driven program that has the following choices (where x and y are inputs the user enters once at the start of the program):

1. Show the even numbers from x to y
2. Show the odd numbers from x to y
3. Show the squares of the numbers from x to y (e.g., if x, y = 2, 4 then: 4 9 16)
4. Exit the program

Solutions?

Remember that solutions are provided for most prac exercises.
These exist to help you learn, not just for copying :)
See the solutions branch here in this repository. Change the branch to "solutions" at the top of the page.
Compare your work to the provided solutions and see if there are any significant differences that you can learn from.

Summary

This section summarises the expectations for this practical.
Each practical includes a list of files or tasks expected.
You are not expected to submit any practical work, since practicals are not marked.

• temperatures.py
• sales_bonus.py
• broken_score.py
• loops.py
• shop_calculator.py
• menus.py