Coding 2 Exercise Instructions

Introduction

In this exercise you will continue working on the app you developed in the Coding 1 Exercise. We will work through the steps below and finish creating our screens and then implement decision-making logic.

Preparation Work

You should read Chapter Four before attempting this exercise.
You should be familiar with the entire chapter, but pay particular attention to if-else statements and nested if statements.
You should have completed working code from the Coding 1 Exercise. If you don't have completed code you can refer to the solution code.

The Exercise

Last week we built out Screen 1, all the question screens and Screen 8, one of the exit screens. This week we are going to implement the decision-making logic. As we do so we will build out the rest of the exit screens.

Make the rest of the exit screens

Last week we created Screen 8. Screens 3, 5 and 7 follow the same formula. Use the instructions for Screen 8 from last week and create question blocks (with event tags) for screens 3, 5 and 7.

Hint: Your code should look something like this

---
# Screen 3
event: MJFexit_screen3
question: Not Eligible
subquestion: |
  According to the *Civil Liability Act* you cannot claim for
  the services you incurred as they were not provided on a
  gratuitous basis.
buttons:
  - Exit: exit
  - Restart: restart
---
# Screen 5
event: MJFexit_screen5
question: Not Eligible
subquestion: |
  You can only be compensated if the person who provided the gratuitous services
  was your parent, spouse, domestic partner or child.
buttons:
  - Exit: exit
  - Restart: restart
---
# Screen 7
event: MJFexit_screen7
question: Not Eligible
subquestion: |
  Your claim must be limited to four times State average weekly earnings.
  State Average weekly earnings are currently $[insert current earnings].
buttons:
  - Exit: exit
  - Restart: restart
---

Comparing Against State Weekly Earnings

Now we need to do some maths (!!!) According to s 58(2) a person is limited as to the amount of damages they can claim for gratuitous services, and this limit is 'not to exceed an amount equivalent to 4 times State average weekly earnings'.

Consequently, we need to know, firstly, what State average weekly earnings are, and then we need to use that figure to calculate the s 58(2) limit.

The term 'State average weekly earnings' is defined is s 3 of the Act and, so you don't have to, I have extracted for you the current State average weekly earnings as of the date this exercise was written. That amount is:

$1,776.90

We will use this figure for this exercise.

First thing we need to do is to let our app know this amount. We do this by setting a variable in a code block, as follows:

---
code: |
  MJFavg_earnings = 1776.9
---

Whenever we need to know what the average weekly earnings are we can just query this variable.

Add this code block to the end of your code.

Next we need to calculate the s 58(2) limit. Arithmetically, this is easy, just multiply MJFavg_earnings by 4. We can do this in another code block.

---
code: |
  MJFs58_limit = MJFavg_earnings * 4
---

notes

If you don't know what the * does in the code block above, please check out 'Data Types' in Chapter Three.
If you don't know what <= means you should also consult Chapter 3. We'll be using these symbols shortly.
We could have put both these statements into a single code block and saved ourselves some typing. However, it's good practice to separate out logically different components into their own blocks.
MJFavg_earnings is set to 1776.9 and not 1776.90 or $1776.90. This is for two reasons.
- Firstly, Python doesn't care whether a number represents money or anything else - it's just a number. You will remember that we had to use the currency() functions in our Coding 1 Preparation exercises.
- Secondly, as MJFavg_earnings is just a number, the trailing 0 is redundant.

OK. Now we're ready to start making decisions!

Decision-making with code

When implementing decisions in code, everything is reduced to a true/false proposition. We usually re-phrase questions so that the answer is true or false. For example, the question 'Were the service provided gratuitous' is expressed as the statement 'The services provided were gratuitous'. If this statement is true, then one path is taken. If this statement is false, then another path is taken.

Sometimes not all questions have a yes or no answer. For example, the question 'Who provided the gratuitous services?' has more than just a yes/no answer. The possible answers, according to our flowchart, are 'Parent', 'Spouse', 'Domestic Partner', 'Child' and 'Someone Else'. In this case we would express each potential answer as a statemend. For example 'The person who provided gratuitous services was my parent', 'The person who provided gratuitous services was my child' and so-on. We could then test each one in turn and then act depending on whether that statement is true or not. To do this we would use an if/elif/else statement. For example:

code: |
  if MJFwho_provided == 'Parent':
    # Move to next step
  elif MJFwho_provided == 'Spouse':
    # Move to next step
  elif MJFwho_provided == 'Domestic Partner':
    # Move to next step
  elif MJFwho_provided == 'Child':
    # Move to next step
  elif MJFwho_provided == 'Someone Else':
    # Display screen 5 as user is not eligible
---

Each statement resolves to true or false.

note

If you look at that if/elif statement closely you'll see that the same action ('move to next step') is performed for every possibility except if the person providing gratuitous servicse is 'Someone Else'. Because this is the case we could re-express the statement to essentially say 'If the person providing gratuitous services is Someone Else then we exit the app, otherwise we move to the next step'. This statement now has only two options - the person either is Someone Else or it isn't. That's an easier if statement to write, and we would do so like this:

code: |
  if MJFwho_provided == 'Someone Else':
    # Display Screen 5 as user is not eligible
  else:
    # Move to next step
---

Making Multiple Decisions

Our Section 58 Calculator chart requires us to make a set of followup decisions after we make our first decision. For example, if we decide the services were gratuitous, then we need to decide if the person who provided those services falls within s 58. If that person does so fall then we need to subsequently decide if the amount claimed falls within the limit.

Let's express this as follows:

if the services are gratuitous, then
if the person who provided them is not someone else, then
if the amount claimed is less than the limit, then the person may be able to claim damages.

You see we need to have three True answers to arrive at the conclusion that the user may be able to claim damages.

We express this sequence of positive decisions in code as follows (using the variables from the example code in the solution)

---
code: |
  if MJFis_gratuitous:
    if MJFwho_provided != 'Someone Else':
      if MJFamount_claimed <= MJFavg_earnings
        exit_screen8
---

You can see that each of the three if statements on lines 3 to 5 mirror the three statements we expressed previously.

note

The symbol != means 'not equal to' in Python. Thus, the code on line 5 can be read as 'if MJFwho_provided is not equal to Someone Else'

Each if statement needs to be indented under its parent so that Python only executes it if the previous statement is true. That is, each if statement sits under its parent if statement's true branch.

You could copy the above code block into your mandatory code block (replacing what is already there). If you did so, and you answered each question correctly then you would arrive at Screen 8 - the 'You May be Eligible' screen.

Replace the contents of your mandatory code block with the nested if statements above
Save and run your app. Enter in the correct answers. Do you arrive at Screen 8?

Populating the False Branches

As we already know, each if statement evaluates to true or false. Consequently, just as every if statement has a true branch it must also have a false branch. This is represented by the else: part of an if-else or an if-elif-else statement.

---
code: |
  if something_is_true:
    # This is the true branch
    # Do the true things
  else:
    # This is the false branch
    # Do the false things
---

---
code: |
  if something_is_true:
    # This is the true branch
    # Do the true things
  elif something_else_is_true:
    # This is another true branch
    # Do different true things
  elif another_thing_is_true:
    # This is another true branch
    # Yes, everyone has their truth!
  else:
    # This is the false branch. All the true branches must 
    # have failed to get here.
    # Do the false things
---

In our app code we have three if statements nested within one another. Each of our if statements also requires a false branch, where we can display exit screens 3, 5 and 7.

Let's do this one at a time.

note

A challenge with nesting if statements is that the corresponding else must line up with the if that it belongs to. As nested if statements get bigger and bigger it becomes a challenge to line up an else that's far away from its if.

This is why we'll start from the bottom of our nested if statements and work out to the top.

False branch if exceeding the s 58(2) limit

For convenience here's what our mandatory code block should look like:

---
mandatory: True
code: |
  if MJFis_gratuitous:
    if MJFwho_provided != 'Someone Else':
      if MJFamount_claimed <= MJFavg_earnings:
        exit_screen8
---

The s58(2) limit decision is the last one made (check the flowchart), and it's consequently the last of our nested if statements. Add a false branch by adding an else: statement that displays screen 7. Your code should look like this:

---
mandatory: True
code: |
  if MJFis_gratuitous:
    if MJFwho_provided != 'Someone Else':
      if MJFamount_claimed <= MJFavg_earnings
        exit_screen8
      else:
        exit_screen7
---

Note how the else lines up with its corresponding if. This is essential and many a student has shed many a tear for want of not lining up their ifs and elses properly.

Please be a happy student.

False branch if Someone else provided the services

The next decision up from the bottom is the eligibility check for who provided the services, which is the test of the value of MJFwho_provided. Our statement tests if MJFwho_provided is not 'Someone Else'. If MJFwho_provided is 'Someone Else' then we need to display exit_screen5.

Modify your code block so that it contains this new false branch

---
mandatory: True
code: |
  if MJFis_gratuitous:
    if MJFwho_provided != 'Someone Else':
      if MJFamount_claimed <= MJFavg_earnings:
        exit_screen8
      else:
        exit_screen7
    else:
      exit_screen5
---

Note where this new else statement appears. It appears below our MJFamount_claimed if/else statement. Why? This is because, the entirety MJFamount_claimed if-else statement is executed inside the true branch of the MJFamount_claimed if-else statement. That is, we're only making a decision about MJFamount_claimed if the MJFwho_provided != 'Someone Else' test evaluates to True.

Note also that we have had to line up this else with the if for MJFwho_provided. You might be able to see now how lining up these ifs and elses can be challenging.

False branch if services are not gratuitous

This is left as an exercise for you. Please be aware of the following

The false branch must sit outside of the true branch for MJFis_gratuitous.
The true branch for MJFis_gratuitous contains two nested if statements. So, our false branch must sit outside these
The else must align with the if for MJFis_gratuitous

Once you have done this you should now have a fully working app!

Testing

Now that we have an app we need to test it. A thorough test involved testing out each possible combinations of answers that could be input into the app to ensure there are no bugs. Thankfully, our app is not too complicated and so this should not take too long.

Test your app. Did you find any bugs?

Solution Code

The solution for the completed app is provided here for you as a reference.

---
mandatory: True
question: Welcome
subquestion: |
  Welcome to the Gratuitous Services Calculator App.  This app helps you to work out if you can claim for gratuitous services provided to you by your family when you were injured.

  Gratuitous services are services that are provided to you for free
buttons:
  - Continue: continue
  - Exit: exit
---
# Mandatory code block. Drives the app
mandatory: True
code: |
  if MJFis_gratuitous:
    if MJFwho_provided != 'Someone Else':
      if MJFamount_claimed <= MJFavg_earnings:
        MJFexit_screen8
      else:
        MJFexit_screen7
    else:
      MJFexit_screen5
  else:
    MJFexit_screen3
---
# Screen 2
question: Gratuitous Services
subquestion: |
  Did you receive gratuitous services while you were injured?

  Gratuitous services are services, such as cleaning or caring provided to you at no cost.
fields:
  - no label: MJFis_gratuitous
    datatype: radio
    choices:
      - I received services and I did not pay for any of them: True
      - I received services but I did pay for them: False
---
# Screen 4
question: Provision of Services
subquestion: |
  Who provided the gratuitous services to you?
fields:
  - no label: MJFwho_provided
    datatype: radio
    choices:
      - Parent
      - Spouse
      - Domestic Partner
      - Child
      - Someone Else
---
# Screen 6
question: Amount Claimed
subquestion: |
  What amount of damages are you claiming for the provision
  of gratuitous services to you while you were injured?
fields:
  - no label: MJFamount_claimed
    datatype: currency
---
# Screen 8
event: MJFexit_screen8
question: You May be Eligible
subquestion: |
  According to section 58 of the *Civil Liability Act* you may be
  able to claim for gratuitous services
buttons:
  - Exit: exit
  - Restart: restart
---
# Screen 3
event: MJFexit_screen3
question: Not Eligible
subquestion: |
  According to the *Civil Liability Act* you cannot claim for
  the services you incurred as they were not provided on a
  gratuitous basis.
buttons:
  - Exit: exit
  - Restart: restart
---
# Screen 5
event: MJFexit_screen5
question: Not Eligible
subquestion: |
  You can only be compensated if the person who provided the gratuitous services
  was your parent, spouse, domestic partner or child.
buttons:
  - Exit: exit
  - Restart: restart
---
# Screen 7
event: MJFexit_screen7
question: Not Eligible
subquestion: |
  Your claim must be limited to four times State average weekly earnings.
  State Average weekly earnings are currently $[insert current earnings].
buttons:
  - Exit: exit
  - Restart: restart
---
code: |
  MJFavg_earnings = 1776.9
---
code: |
  MJFs58_limit = MJFavg_earnings * 4
---

Introduction​

Preparation Work​

The Exercise​

Make the rest of the exit screens​

Comparing Against State Weekly Earnings​

Decision-making with code​

Making Multiple Decisions​

Populating the False Branches​

False branch if exceeding the s 58(2) limit​

False branch if Someone else provided the services​

False branch if services are not gratuitous​

Testing​

Solution Code​

Introduction

Preparation Work

The Exercise

Make the rest of the exit screens

Comparing Against State Weekly Earnings

Decision-making with code

Making Multiple Decisions

Populating the False Branches

False branch if exceeding the s 58(2) limit

False branch if Someone else provided the services

False branch if services are not gratuitous

Testing

Solution Code