1. Lecture 5 – Unit 1 – Chatbots Python – More on Conditional statements
CMPT 120
Lecture 5 – Unit 1 – Chatbots
Python – More on Conditional statements

2. Review from last lecture
1. What is wrong with this code?
3_colours = ["blue", "green", "white", "pink"]
2. How could this code be improved?
favBand = input()
print("Oh, I like this band!")
3. Why do we want to put an import statement at the beginning (top) of a program?
-> see next two slides
4. When a program executes, what is first executed?

3. Import at the top of program?
Functions (like choice())
from the import module
can be used in this
section of my program

4. Import further down?
Functions (like choice())
from the import module
can not be used in this
section of my program
Notice that the yellow section is smaller here than on the previous slide meaning that the section of my program in which functions (like choice()) from the import module can be used is reduced. Why not maximize this section? To do so, import at the top of your program!

5. Review from last lecture
Execution Flow
Execution flow is the path the Python Interpreter takes when it executes our program
When we execute our program, the Python Interpreter starts interpreting each statement (line) of our program from its very top down to its last line, proceeding in a sequential fashion (one line at a time, top to bottom)

6. Last Lecture, we did …

7. About commenting out code
You can comment
out the code that
works so you focus on testing the new code.
Don’t forget to remove
the # sign once all your
code has been tested!
Tip: CTRL+/

8. Homework – from last lecture
Problem Statement:
Write a chatbot that prints random cookie fortune statements

9. Let’s introduce Branching (Python Conditional statements)
Problem Statement
Make a chatbot that asks a user how their day is going, and make a comment that changes depending on how the user answered
Also think about the various branches in web sites. If you say YES, then continue with your purchase. If you click CANCEL, you’re back to a different path.
Good!
How’s it going?
Not great...

10. Your turn! Problem Statement
Modify the How's it Going chatbot to use 2 "elif" statements

11. Boolean Expressions -> Homework for next lecture
Problem Statement
Write a login program, which allows a user to login in with a password

12. Review: Conditional statements
if statement
Syntax #1:
Boolean expression
This small empty space made of a few white space (or blank) characters is called an indentation and its presence is very important in a conditional statement in Python.

13. Review: Conditional statements
if else statement
Syntax #2:
Indentation
Boolean expression

14. Review: Conditional statements
nested if statement
nested if statement

15. Review: Conditional statements
chained if statement

16. Review: How nested if works
Conditional Statement – nested if statement
if weekday == 0:
print("That's Monday!")
else:
if weekday == 1:
print("That's Tuesday!")
if weekday == 2:
print("That's Saturday!")
if weekday == 3:
print("That's Sunday!")
print("Your number was not between 0 and 3 :( !")
“Green” if else is nested in the “blue” if else
“Red” if else is nested in the “green” if else
“Black” if else is nested in the “red” if else

17. Review: How chained if works
Conditional Statement – chained if statement
if weekday == 0:
print("That's Monday!")
elif weekday == 1:
print("That's Tuesday!")
elif weekday == 2:
print("That's Saturday!")
elif weekday == 3:
print("That's Sunday!")
else:
print("Your number was not between 0 and 3 :( !")
“Green” if elif is chained to the “blue” if elif
“Red” if elif is chained to the “green” if elif
“Black” if else is chained to the “red” if elif

18. Next Lecture
We’ll continue practicing using conditional statements in our Python programs
We shall also play around Boolean values and Boolean expressions