Lab 03: Booleans and Assert

General Information

Submitting to the Auto-Grader

For auto-grading homework assignments in the course, we use Gradescope.

General Submission Info

When submitting files to Gradescope, you need to submit all the files you want graded at once.

You can do this in several ways:

Select all files you want to submit and drag and drop them in the submission area when prompted.
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Gradescope will look for files with specific names, and those names are case-sensitive. So if in the instructions we ask for a file named hello.py, then Gradescope will not recognize Hello.py, hello.txt, or hello.py.txt.

Group Submissions

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They should then add the other members to that submission. On the Gradescope page for a submission there should be a "+ Add Group Member" button by the name in the upper-right.

This is important because if multiple people submit, our similarity checker will see identical submissions and flag that.

Unlimited attempts

You have unlimited attempts for our auto-graded assignments.

This means that you should submit early and often in order to be confident that code you are writing as you go passes all of our tests.

Academic Honesty

All work that is completed in this assignment is your own group's. You may talk to other students about the problems you are to solve, however, you may not share code in any way, except with your partner(s). What you submit must be your own group's work.

You may not use any code that is posted on the internet. If you are not sure it is in your best interest to contact the course staff. We will be using software that will compare your code to other students in the course as well as online resources. It is very easy for us to detect similar submissions and will result in a failure for the exercise or possibly a failure for the course. Please, do not do this. It is important to be academically honest and submit your work only. Please review the UMass Academic Honesty Policy and Procedures so you are aware of what this means.

Copying partial or whole solutions, obtained from other students or elsewhere, is academic dishonesty. Do not share your code with your classmates, and do not use your classmates' code. If you are confused about what constitutes academic dishonesty you should re-read the course policies. We assume you have read the course policies in detail and by submitting this project you have provided your virtual signature in agreement with these policies.

About

This lab has you making some boolean expressions and practicing the use of asserts.

This lab has you use assert both to ensure the functions have received legal arguments, and as a means of checking that the result returned by a function is reasonable.

Learning Objectives

Practice building up boolean expressions
See a 2+ variable truth table
Practice using asserts as a sanity check

Estimated Size

4 functions:

A one-liner with two asserts
Another one-liner, with three asserts
Another one-liner, though could be broken up more. Has one assert.
A function with 3 asserts

Preamble

This lab centers around boolean expressions and assert statements.

Remember that assert is not a function, it takes an expression to assert is true, and optionally a string to print if the assertion is violated.

For instance:

assert 0 <= x, "x is negative"

If x were -5 in the above example, the program would terminate with an error message AssertionError: x is negative.

This can be used to ensure the arguments passed to a function are legal. Imagine you had a function that would perform some arithmetic, you could use assert to ensure the arguments are numbers:

def do_some_math(x:float, y:float) -> float:
  assert type(x) == int or type(x) == float
  assert type(y) == int or type(y) == float
  # do something mathematical

These asserts would trigger if illegal arguments were passed to the function. In a finished working version of the code, they would hopefully not ever trigger.

You can also use asserts to create "tests" or "validation functions". Imagine you had a function that gave you a random number in a range. You could make a validation function full of asserts to ensure it is working correctly, for instance:

def validate_get_number_in_range(lower_bound:int, upperbound:int, number:int) -> None:
  # (return is None, because it will either throw an error or do nothing)
  assert lower_bound <= number
  assert number <= upper_bound

# ... later in code
# Some function we want to use:
x = get_number_in_range(lower_bound, upper_bound)
# Making sure/testing it satisfies some criteria:
validate_get_number_in_range(lower_bound, upper_bound, x)
# Do something with x

In a working version of the code, this would never trigger, but while writing code it can help catch bugs (like in the get_number_in_range() function above).

Assignment

0. Set up file named `school.py` (1 point)

Make a file named school.py, all your work should be in that file and that is what you will submit to Gradescope.

Don't forget author comments at the top, e.g.:

# Authors   : Jared Yeager,         Tim Richards
# Emails    : jyeager@cs.umass.edu, richards@cs.umass.edu
# Spire IDs : 31415926,             27182818

1.1. Implement `different_names()` (1 point)

Write a function named different_names() that takes in two strings, and returns True if they are different and False if they are the same.

Capitalization matters, "Joe" is not the same as "joe", for this function. And they are not the same in terms of string comparison with == (so you basically don't need to worry about it).

Hints

Boolean expressions will be useful here.

Just like arithmetic expressions and values, you can store boolean values and the results of boolean expressions in variables, e.g., in_range_01 = 0 <= x and x <= 1.

Testing

Call the function, get the output, print the output. Try it with names that are the same, try it with names that are different.

1.2. Add `assert`s to `different_names()` (1 point)

assert allows you to force a guarantee about the state of your code beyond a point (by terminating the program if that guarantee is not met).

We can use this for testing, but we can also use to it to reject illegal inputs to a function.

We want to ensure that the inputs to the different_names() are both strings (type equal to str). So can add asserts requiring this to be so. This way, if the inputs are not strings, then you get a clear termination of the program with an error message and not have less clear error or quiet misbehavior.

So add asserts to this function to ensure the inputs are of type str. These should be at the beginning of the function, like in the second code block in the preamble section.

Note: You are editing the existing function, not making a new one.

Hints

If it hasn't come up, there is function called type() that gives you the type of something.

And the result of that can be compared against something like int, float, or str.

See the preamble for an example.

2.1. Implement `three_unique_names()` (1 point)

Write a function named three_unique_names() that takes in three strings, and returns True if they are all different from each other and False if any two are the same.

Capitalization still matters (e.g., "Joe" and "joe" are different in the eyes of this function and the == operator).

Hints

You can use your implementation of different_names() if you'd like.

Testing

To cover all the cases, you'd want to test when all names are the same, every passible combination of two names is the same and one is different (3 ways this can happen), and when all 3 names are different.

2.2. Add `assert`s to `three_unique_names()` (1 point)

Add asserts to this function to ensure the inputs are of type str. You want to ensure an assertion error is any of the three inputs are not of type str.

These should be at the beginning of the function, like in the second code block in the preamble section.

Note: You are editing the existing function, not making a new one.

Extra

Depending on how you implemented this function, you may not need to add asserts at all because of the asserts in different_names().

But, be warned, if you have function calls in an and or or statement, then they may not be called due to "short circuiting". This is where the expression on the left of an and evaluates to False, and so the computer knows the whole thing is False and thus doesn't check the expression on the right. Ditto the left expression of an or evaluating to True.

3.1. Implement `school_open()` (2 points)

Write a function named school_open() that takes in variables (that I will call) day, is_holiday, is_snowy, and is_plowed:

day is an int in the range of 1 to 7 (inclusive). 1 represents Sunday, 2 Monday, ..., 7 Saturday.
is_holiday is a boolean that is True if and only if today is a holiday.
is_snowy is a boolean that is True if and only if there is snow.
is_plowed is a boolean that is True if and only if any snow has been plowed. If is_snowy is False, then this variable may be either True or False and it doesn't matter.

This function should return True if and only is school is open.

School can't be open on a weekend (Saturday or Sunday). School can't be open on a holiday. School can't be open if it has snowed and not been plowed. Otherwise, school is open.

But forget words, have a big ol' truth table:

`is_weekday`	`is_holiday`	`is_snowy`	`is_plowed`	`is_open`
True	True	True	True	False
True	True	True	False	False
True	True	False	True	False
True	True	False	False	False
True	False	True	True	True
True	False	True	False	False
True	False	False	True	True
True	False	False	False	True
False	True	True	True	False
False	True	True	False	False
False	True	False	True	False
False	True	False	False	False
False	False	True	True	False
False	False	True	False	False
False	False	False	True	False
False	False	False	False	False

Hints

The challenge of this is translating the words to code, and it's hard to give hints for that.

Perhaps a starting point might be asking "is school open if A and B and C and ... or if A or B or C or ..., and then trying to figure out what those A, B, C, et cetera are in code.

Also, if you like the is_weekday value, then make you want a helper function that takes in a day as return True if (and only if) it is a weekday.

Testing

*Sigh*, my actual recommendation involves a for loop and printing out your empirical truth table, but we don't have loops yet.

When you can't check every case, you can still test a collection of representative cases, and maybe also a bunch of random cases.

For representative cases, you want to test the variable factors (weekend, holiday, and plowing stuff). As a control, I would start with some weekday, no holiday, no snow, no plow; make sure that's true. Then test toggling the day, the holiday, then snow, and the plow given snow. Basically, this slice of the truth table:

`is_weekday`	`is_holiday`	`is_snowy`	`is_plowed`	`is_open`
True	False	False	False	True
False	False	False	False	False
True	True	False	False	False
True	False	True	False	False
True	False	True	True	True

(I'd also want play around with the day a bit to catch if I've messed up computing the helper variable is_weekday)

I'd even go as far as making a helper function that takes the inputs for school_open(), passes those to school_open(), saves the output, and prints a line of the truth table in an aesthetically pleasing manner.

For doing random sample testing, import random, and then random.randint(1,7) and multiple uses of random.choice([True,False]) would allow you to generate a random case.

3.2. Add `assert`s to `school_open()` (2 points)

Add an assert to school_open() to ensure that the day parameter is in the 1 to 7 range. And think for a bit about how your solution would have treated a number outside the range. It would probably have run without issues, but something wrong would be happening in some sense without us being aware of it.

This should be at the beginning of the function, like in the second code block in the preamble section.

(If you want, feel free to ensure that the other values are all of type bool)

Note: You are editing the existing function, not making a new one.

4. Implement `verify_school_open()` (2 points)

Another way to test the above function is with a sanity check/validation test using assert.

This approach is demonstrated in the third code block in the preamble section.

When you pass day, is_holiday, is_snowy, and is_plowed to the school_open() function, you get back a result; call it is_open.

There are several things that should be true about these variables:

You should not have a case where day represents a weekend (is_weekday is False) and is_open is True
You should not have a case where is_holiday is True and is_open is True
You should not have a case where is_snowy is True, is_plowed is False, and is_open is True

These will become the asserts for the validation function.

Make a function with the signature

verify_school_open(day, is_holiday, is_snowy, is_plowed, is_open)

This function should assert the three things above. This will allow you to run code of the form:

is_open = school_open(day, is_holiday, is_snowy, is_plowed)
verify_school_open(day, is_holiday, is_snowy, is_plowed, is_open)

Here, an incorrect implementation of school_open() has a chance of triggering the asserts in verify_school_open().

(Naturally, the implementation of verify_school_open()) may not be correct, but figuring out why there is a contradiction between the two can still be informative.)

Extra

So where did those assertions come from.

Here are the original instructions:

School can't be open on a weekend (Saturday or Sunday).
School can't be open on a holiday.
School can't be open if it has snowed and not been plowed.
Otherwise, school is open.

In logic terms the first three are respectively equivalent to:

not weekday implies not open
holiday implies not open
snowed and not plowed implies not open

"A implies B" is logically equivalent to "(not A) or B":

weekday or not open
(not holiday) or not open
not (snowed and not plowed) or not open

Pulling the not out via reverse DeMorgans:

not (not weekday and open)
not (holiday and open)
not (snowed and not plowed and open)

Note that since I only translated 3 conditions, there are some illegal combinations that can get through the asserts. Violations of the "otherwise school is open" rule. False closures are completely missed.

Lab 03: Booleans and Assert

General Information

General Submission Info

Group Submissions

Unlimited attempts

About

Learning Objectives

Estimated Size

Preamble

Assignment

0. Set up file named `school.py` (1 point)

1.1. Implement `different_names()` (1 point)

1.2. Add `assert`s to `different_names()` (1 point)

2.1. Implement `three_unique_names()` (1 point)

2.2. Add `assert`s to `three_unique_names()` (1 point)

3.1. Implement `school_open()` (2 points)

3.2. Add `assert`s to `school_open()` (2 points)

4. Implement `verify_school_open()` (2 points)

Grading Scale

1: Below Standards: 0-3 points

2: Approaching Standards: 4-7 points

3: Meeting Standards: 8-9 points

4: Exceeding Standards: 10-11 points

Lab 03: Booleans and Assert

General Information​

General Submission Info​

Group Submissions​

Unlimited attempts​

About​

Learning Objectives​

Estimated Size​

Preamble​

Assignment​

0. Set up file named school.py (1 point)​

1.1. Implement different_names() (1 point)​

1.2. Add asserts to different_names() (1 point)​

2.1. Implement three_unique_names() (1 point)​

2.2. Add asserts to three_unique_names() (1 point)​

3.1. Implement school_open() (2 points)​

3.2. Add asserts to school_open() (2 points)​

4. Implement verify_school_open() (2 points)​

Grading Scale​

1: Below Standards: 0-3 points​

2: Approaching Standards: 4-7 points​

3: Meeting Standards: 8-9 points​

4: Exceeding Standards: 10-11 points​

General Information

General Submission Info

Group Submissions

Unlimited attempts

About

Learning Objectives

Estimated Size

Preamble

Assignment

0. Set up file named `school.py` (1 point)

1.1. Implement `different_names()` (1 point)

1.2. Add `assert`s to `different_names()` (1 point)

2.1. Implement `three_unique_names()` (1 point)

2.2. Add `assert`s to `three_unique_names()` (1 point)

3.1. Implement `school_open()` (2 points)

3.2. Add `assert`s to `school_open()` (2 points)

4. Implement `verify_school_open()` (2 points)

Grading Scale

1: Below Standards: 0-3 points

2: Approaching Standards: 4-7 points

3: Meeting Standards: 8-9 points

4: Exceeding Standards: 10-11 points