1. Lecture 7 – Unit 1 – Chatbots Python – For loops + Robustness
CMPT 120
Lecture 7 – Unit 1 – Chatbots
Python – For loops + Robustness

2. Homework - Show Case Problem Statement
Write a login program, which allows a user to login in with a password
Thank you for sending your link

3. Review - Little Exercise version 1 + Answers
if condition 1 : if condition 2 : some statements A if condition 3 : some statements B else : some statements C if condition 4 : some statements D some statements E some statements F some statements G
1. Which statements are executed if condition 1 is False?
Answer: F and G
2. Which statements are executed if condition 1 is
True and condition 2 is
False?
Answer: E and G

4. Review - Little Exercise version 2 + Answers
if condition 1 : if condition 2 : some statements A if condition 3 : some statements B else : some statements C if condition 4 : some statements D some statements E some statements F some statements G
1. To execute statements A B D G, to what Boolean value would conditions 1, 2, 3 and need to evaluate?
Answer: condition 1, 2, 3,
and 4 would need to be True.
2. To execute statements A B C G, to what Boolean value would conditions 1, 2, 3 and need to evaluate?
Answer: It is impossible to
have statements A B C G
executed together.

5. Reading Review What does the string strip function (method) do?
What string function (method) should we use to replace all occurrences of “8” in a string with “9”?
What could be wrong with this code?
if reply.lower().strip(" ") == "GOOD"
print("Good!")
What does this code output?
movies = ["Superman", "Frozen", "X-Men"]
print("x-men" in movies)

6. Review - Examples of Boolean
"great" == "Great" -> False
"Great!" == "Great" -> False
"Great!" == "Great!" -> True
"23" < "19" -> False 
"100" < "19" -> True 
How does this work?
How can we compare characters?

7. ASCII Code (part of Unicode)

8. Reading Review What we can do with the "in" keyword for lists

9. Let’s build a simple game!
Problem Statement
Write a guessing game, which allows a user to guess a number between 1 and 10
My solution:

10. Guessing Game Testing our guessing game:
Test case 1 : input != number to guess
Test case 2 : input == number to guess
Test case 3 : invalid input -> 53 (outside range)

11. Your turn! Problem Statement
Write a guessing game, which allows a user to guess a number between 1 and 10
Requirements:
Let’s make your guessing game more responsive
How?
By telling the user when she/he has entered a number that was < 1
“You have entered a number < 1!”
or > 10
“You have entered a number > 10!”

12. Improving our Guessing Game
Problem Statement
Write a guessing game, which allows a user to guess a number between 1 and 10
Requirements:
Let’s make your guessing game more robust
So it does not crash when the player enters unexpected input like “banana”
My Solution:

13. You have 3 guesses!
Wouldn’t it be nice to play our guessing game many times without having to press Run over and over again?
Problem Statement
Write a guessing game, which allows a player to guess a number between 1 and 10 in 3 guesses!
My Solution:
Use a for loop (iteration)

14. Review – Terminology related to functions
We call a function by name
Example of a function call:
userName = input("Please, enter your name: ")
The name of the function is input
The expression in parentheses is called the argument of the function
We say that a function takes an argument(s)
The result of the function is what the function produces
In the above example, the result of the function is what the user has typed, i.e., her/his name, which is assigned to userName
‘Anne’
We say that a function returns a result and the result is called the returned value

15. Review – type( ): another useful function
Built-in function
Syntax: type(<expression>)
How it works:
The expression is evaluated
type(…) is called with the result of the expression as its argument
type(…) returns a value which is the data type of its argument, i.e., the result of the expression
Examples:
type(123)
type("Hello")
type("123")
pi = 3.14
type(pi)

16. How to construct a condition?
SYNTAX: <operand> <operator> <operand>
Relational operators (or comparison operators)
< less than
> greater than
<= less than or equal to
>= greater than or equal to
== equal to
!= not equal to
Variable
Literal value
-> both of type string, integer or float
Variable
Literal value
-> both of type string, integer or float
Result of conditional expression: True or False
Relational operators (< , >=, ==, …) may connect expressions evaluating to different types of values

17. How to construct a condition?
SYNTAX: .<method>(…) <function>(…) operator
Example:
<string>.isdigit( ) <string>.isalpha( )
etc…
Example:
all(…)
etc…
Example: in
containment test operator
Result of conditional expression: True or False
We have built-in functions returning numerical values: len(“hello”) returns 5
int(“5”) returns 5
We have methods returning numerical values: “hello”.find(“lo”) returns 3
Similarly, we have built-in functions returning Boolean values:
all([1<2,2<4,5==5]) returns True
We have methods returning Boolean values:
“123456”.isdigit() returns True
“123456”.isalpha() returns False

18. What if we have more than 1 conditions?
In our Guessing Game
If the user enters a guess (a number) between 1 and 10 -> valid data
If the user enters a guess < 1 or > 10 -> invalid data
Guardian code (input validation code):
if userGuess < 1 or userGuess > 10 :
print("Your guess should be a
number between 1 and 10...")
# then terminate program
else :
...
This is called a
compound
condition: a
condition that
Is composed
of > 1 condition.

19. What if we have more than 1 conditions?
We could also create the following guardian code (input validation code):
if userGuess >= 1 and userGuess <= 10 :
# Did the user guess correctly?
# Display appropriate message
if number == userGuess :
print("Wow! You got it!")
else :
print("Sorry! You missed! The number was %d." %number)
...
compound
condition

20. How to construct a logical expression (compound condition)?
Conditions (Boolean expressions, i.e., expressions producing Boolean values), can be connected via the logical operators
and, or, not
creating logical expressions
Such logical expressions are called compound conditions

21. How to construct a logical expression (compound condition)?
SYNTAX for
and & or: <operand> <logical_operator> <operand>
not: not <operand>
Logical operators
operand
and or
operand
Boolean expression
Boolean expression
not
operand
Result of compound conditional expression: True or False
Boolean operators and, or must connect two Boolean expressions Boolean operator not must be applied to one Boolean expression

22. How to evaluate a logical expression (compound condition)?
Boolean truth table:
and truth table
or truth table
not truth table
Source:
an-introduction-to-software-development-software-development-midterm-review

23. Next Lecture
Let’s see how much we have learnt so far by having a little practice exam!
We’ll have plenty of help while going through this activity