Description
Boolean expressions, if statements,
debugging, and …
1
What is in this lab?
1. This lab bas 3 Tasks (3rd task has several parts). You should try
to do these parts at home.
Task 2 and 3 are in the interactive textbook. Watch the
video I provided (follow the link at page 7) before doing
these two tasks.
2. And 5 programming exercises (0 to 4)
The slides that are included here but do not explain either Tasks
or Programming exercises are there as reminder of some relevant
material that is needed for this lab.
2
Lab 3 overview
• Open a browser and log into Brightspace
• On the left hand side under Labs tab, find lab3 material
contained in either lab3-students.zip or lab3-studnets.pdf file
• Download that file to the Desktop and open it.
• Read slides one by one and follow the instructions explaining
what to do. When stuck ask for help from TA. Ideally you
should try to complete some, or all of this, at home and then
use the lab as a place where you can get help with things you
may have had difficulties with.
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Before starting, always make sure you
are running Python 3
This slide is applicable to all labs, exercises, assignments … etc
ALWAYS MAKE SURE FIRST that you are running Python 3. That is,
when you click on IDLE (or start python any other way) look at
the first line that the Python shell displays. It should say Python 3.
(and then some extra digits)
If you do not know how to do this, read the material provided
with Lab 1. It explains it step by step
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div // and mod % operators in Python
If uncertain, here is how to compute a//b (i.e. integer division) and a%b (i.e remainder)
1. Compute x=a/b
2. a//b is then equal to the whole (i.e integer) part of x.
More precisely a//b is equal the integer that is closest to a/b
but not bigger than a/b
3. a%b is equal to a – (a//b) * b
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Task 1
What is the type and value of each of the following expressions in Python? Do this
in you head (and/or paper) first. The check both columns in Python shell. eg. You
can test what kind of value the first expression returns by typing
type(13*0.1) in Python shell
Expression Type Value
13 * 0.1 float 1.3
int(13) * 0.1
13 * int(0.1)
int(13 * 0.1)
13 % 7
7 % 13
6%3
0%15
6//2.5
6%2.5
2<3== 4<5
Interactive textbook (Reminder)
Here is a link to the interactive textbook:
https://runestone.academy/runestone/static/thinkcspy/index.html
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Task 2: Debugging
Follow this link, and read, run and do the exercises there:
https://runestone.academy/runestone/static/thinkcspy/Debugging/HowtoAvoidDebugging.html
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An example used in the above link refers to the following problem from
Chapter: Simple Python Data, Section: Exercises, Question 3:
https://runestone.academy/runestone/static/thinkcspy/SimplePythonData/Exercises.html
Many people keep time using a 24 hour clock (11 is 11am and 23 is
11pm, 0 is midnight). If it is currently 13 and you set your alarm
to go off in 50 hours, it will be 15 (3pm). Write a Python program
to solve the general version of the above problem. Ask the user
for the time now (in hours), and then ask for the number of hours
to wait for the alarm. Your program should output what the time
will be on the clock when the alarm goes off.
Programming exercise 0:
More debugging and coding
Open file q0.py and solve the 3 programming exercises as
instructed.
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Boolean Expressions
Boolean expressions evaluate to True or False
Logical/Boolean operators in Math and Python:
Math Python
AND and
OR or
NOT not
Here is how your compare two variables a and b in Math and Python
Math Python
a = b a == b
a ≤ b a <= b a ³ b a >= b
a ¹ b a != b
Truth table
A TRUTH TABLE for a compound Boolean expression shows
the results for all possible combinations of the simple expressions:
Testing if two strings are equal
For one of the programming exercise you will need to know that how to
compare if two strings are equal. You can do that simply buy using ==
operator. Here are some examples
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>>> ‘A’==‘A’
True
>>> ‘Anna’==‘Anna’
True
>>> ‘Anna’=‘anna’
False
>>> a=‘June’
>>> a==‘june’
False
>>> a==‘June’
True
>>> b=‘Ju’ + ’ne’
>>> a==b
True
ps. Do not copy paste the above into python shell. It will likely give you syntax
errors since quotes do not copy/paste correctly from Word.
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Examples of compound boolean expressions:
• This is how you would test if age is at least 18 and at most 65:
age>=18 and age <= 65 • not is an operator to negate the value of a simple or compound Boolean expression. Suppose age = 15. Then: age > 16 evaluates to False, and not(age > 16) evaluates to True
• Suppose day refers to a string which is a day of a week. Here is how you would
test if day is a weekend:
day==“Saturday” or day==“Sunday”
• Here are two ways to test if age is less than 18 or greater than 65. Think
about the 2nd one
– 1st way: age<18 or age > 65
– 2nd way: not(age>=18 and age <= 65) Task 3: if statements Follow all the links below. Read, run and do the exercises in each of them. No need to watch the videos. Boolean Expressions https://runestone.academy/runestone/static/thinkcspy/Selection/BooleanValuesandBooleanExpressions.html Logical/Boolean operators https://runestone.academy/runestone/static/thinkcspy/Selection/Logicaloperators.html PrecedenceOfOperations https://runestone.academy/runestone/static/thinkcspy/Selection/PrecedenceofOperators.html Two-way if statement: https://runestone.academy/runestone/static/thinkcspy/Selection/ConditionalExecutionBinarySelection.html One-way if statement: https://runestone.academy/runestone/static/thinkcspy/Selection/OmittingtheelseClauseUnarySelection.html Nested if statement: https://runestone.academy/runestone/static/thinkcspy/Selection/Nestedconditionals.html Chained conditionals (i.e elif) https://runestone.academy/runestone/static/thinkcspy/Selection/Chainedconditionals.html 14 ITI 1120 DOCSTRINGS For all the python functions that you will write in the following questions (and in the future) make sure you document your functions by writing docstrings including the type contract (as we have done in class). Test if you docstrings appear as help of your function by running help(your_function_name) in python shell. 15 ITI 1120 Programming exercises: Question 1 Write function called pay that takes as input an hourly wage and the number of hours an employee worked in the last week. The function should compute and return the employee’s pay. Overtime work should be paid in this way: Any hours beyond 40 but less than or equal 60 should be paid at 1.5 times the regular hourly wage. Any hours beyond 60 should be paid at 2 times the regular hourly wage. Important: Important: Note that I did not give you either the number of parameters or the names of parameters. You will have to figure it out on your own for this function. Looking at the test examples below should help. 16 Example tests: >>> pay(10, 35)
350
>>> pay(10, 45)
475.0
>>> pay(10, 61)
720.0
Programming exercises: Question 2
Rock, Paper, Scissors is a two-player game in which each player chooses one
of three items. If both players choose the same item, the game is tied.
Otherwise, the rules that determine the winner are:
(a)Rock always beats Scissors (Rock crushes Scissors)
(b) Scissors always beats Paper (Scissors cut Paper)
(c) Paper always beats Rock (Paper covers Rock)
Write a function called rps that takes the choice ‘R’, ‘P’, or ‘S’ of
player 1 and the choice of player 2, and returns −1 if player 1 wins, 1 if player
2 wins, or 0 if there is a tie.”
Note that I did not give you either the number of parameters or the names of
parameters. You will have to figure it out on your own. Looking at the
example runs below should help too:
Example tests:
>>> rps(‘R’, ‘P’)
1
>>> rps(‘R’, ‘S’)
-1
>>> rps(‘S’, ‘S’)
0
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Programming exercises: Question 3a
Open a new file with IDLE. Write a program that has a function called
is_divisible
• The function is_divisible has two input parameters that are integers
n and m and returns True if n is divisible by m and False otherwise.
• Outside of that function, your program should interact with the user to get
two integers. To determine if the 1st is divisible by the 2nd it should call
is_divisible function. It should print a message explaining the result.
Two example tests (one on the left and one on the right)
>>>
Enter 1st integer:
9
Enter 2nd integer:
3
9 is divisble by 3
>>>
Enter 1st integer:
8
Enter 2nd integer:
3
8 is not divisble by 3
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Programming exercises: Question 3b
Open a new file with IDLE. Write a program that has two functions one called
is_divisible and the other called is_divisible23n8
•The function is_divisible is the same as in the previous questions so
you can copy/paste it to the beginning of the new file.
•The function is_divisible23n8 has one input parameter, an integer.
It should return string “yes” if the given number is divisible by 2 or 3 but
not 8. Otherwise it should return a string “no”. Your function
is_divisible23n8 must use, i.e make a call to, is_divisible
•Outside of that function, your program should interact with the user to get
one integer. It should call is_divisible23n8 function to deterimen if
the number the user gave is divisible by 2 or 3 but not 8. It should print a
message explaining the result.
>>>
Enter an integer: 18
18 is divisible by 2 or 3 but not 8
>>>
Enter an integer: 16
It is not true that 16 is divisible by 2 or 3 but not 8
>>>
Enter an integer: 3
3 is divisible by 2 or 3 but not 8
Bonus programming exercises:
For those who are done and want to more programming
exercises for the lab or home, follow this link and complete
any, or ideally all, exercises there:
https://runestone.academy/runestone/static/thinkcspy/Selection/Exercises.html
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