booleaN

and

conditional logic

Objectives

  • Learn how to use comparison operators to make a basic program
  • Learn how to get user input in Python
  • Learn about "Truthiness"

There is a built-in function in Python called "input" that will prompt the user and store the result to a variable.

User Input

name = input("Enter your name here: ")
Enter your name here: 
Tyrion Lannister
name
'Tyrion Lannister'

BOOLEAN EXPRESSIONS

Conditional logic using if statements represents different paths a program can take based on some type of comparison of input.

Conditional Statements

if some condition is True:
    do something
elif some other condition is True:
    do something
else:
    do something

Conditional logic using if statements represents different paths a program can take based on some type of comparison of input.

Conditional Checks

if name == "Arya Stark":
    print("Valar Morghulis")
elif name == "Jon Snow":
    print("You know nothing")
else:
    print("Carry on")
name
"Jon Snow"
*
"Arya Stark"
"You know nothing."
"Valar Morghulis."
"Carry on."

In Python, all conditional checks resolve to True or False.

Truthiness

x = 1
x is 1  # True
x is 0  # False

We can call values that will resolve to True "truthy", or values that will resolve to False "falsy".

Besides False conditional checks, other things that are naturally falsy include: empty objects, empty strings, None, and zero.

Here is a list of comparison operators.

In the examples, a = 1 and b = 1

Comparison Operators

Op What it does Example
== Truthy if a has the same value as b a == b  # True
!= Truthy if a does NOT have the same value as b a != b  # False
>
<		 Truthy if a is greater than b
Truthy if a is less than be b 		a > b  # False
a < b  # False
>=
<=		 Truthy if a is greater than or equal to b
Truthy if a is less than or equal to b 		a >= b  # True
a <= b  # True

In Python, the following operators can be used to make Boolean Logic comparisons or statements:

Logical Operators

Op What it does Example
and Truthy if both a AND b are true (logical conjunction) if a and b:
    print(c)
or Truthy if either a OR b are true (logical disjunction) if am_tired or is_bedtime:
    print("go to sleep")
not Truthy if the opposite of a is true (logical negation) if not is_weekend:
    print("go to work")

"It depends upon what the meaning of the word 'is' is."

is vs. "=="

- Bill Clinton

In python, "==" and "is" are very similar comparators, however they are not the same.

a = 1
a == 1  # True
a is 1  # True
a = [1, 2, 3]  # a list of numbers
b = [1, 2, 3]
a == b  # True
a is b  # False
c = b
b is c  # True

"is" is only truthy if the variables reference the same item in memory

BOUNCER CODE-ALONG

(with a nested conditional)

The following program, bouncer.py, determines whether the user can enter the club or not.

Bouncer Solution 1

age = input("How old are you: ")
if age:
	age = int(age)
	if age >= 18 and age < 21: 
		print("You can enter, but need a wristband!")
	elif age >= 21:
	    print("You are good to enter and can drink!")
	else: 
		print("You can't come in, little one! :(")
else:
	print("Please enter an age!")

It also checks to make sure the user entered an age

The following program, bouncer.py, determines whether the user can enter the club or not.

Bouncer Solution 2

age = input("How old are you: ")
if age:
	age = int(age)
	if age >= 21:
	    print("You are good to enter and can drink!")
	elif age >= 18:
	    print("You can enter, but need a wristband!")
	else: 
		print("You can't come in, little one! :(")
else:
	print("Please enter an age!")

Slightly refactored conditional logic

Recap

  • Conditional logic evaluates whether statements are truthy or not
  • Conditional logic can control the flow of a program
  • We can use comparison and logical operators to make conditional if statements

ROCK 🤜🏻

PAPER ✋🏽 SCISSORS ✌🏾

"Try this on your own or treat it as a code-along"

THe "Basic" Version

...rock...
...paper...
...scissors...
(enter Player 1's choice): rock
(enter Player 2's choice): paper 
SHOOT!
player2 wins

It may not be the most fun game ever made

THe "Less Basic" Version

...rock...
...paper...
...scissors...
(Enter your choice): paper
The computer plays: scissors
Computer wins!

Featuring the dumbest "AI" ever

HINT!

Research randint

You will need to import something

🙀

YOUR TURN