2a: Comparisons and conditionals

1. Homework check?
2. Bit more about booleans
3. Conditionals
4. The "in" operator

🎉Table of contents with working links🎉

1. Homework check?

2. Bit more about booleans

2.1. Boolean value

check = True

print(type(check))

(N.B.: not how we can check the data type of the variable!)

2.2. Boolean expressions:

An expression is a combination of variables, operators, and values that lead to a single result.

A boolean expression is an expression that is either true or false: it leads to a boolean value.

Last Friday: boolean expressions with relational operators:

print(5 >= 3)

Today we add: boolean expressions with logical operators that allow us to combine boolean values and/or expressions:

#print(not False or False)

print(3 > 2 and 4 > 5)

Note that logical operators are meant to work with boolean values or expressions.

But Python is tolerant and will also treat …
… the integer 0
… the float 0.0
… the string ""
… as False.
The rest of the integers, floats and strings are treated as True

if "hi all":
    print("this is true")

3. Conditionals

3.1. Conditional execution

Simplest form of an if-statement:

if 0:
    print("this is considered as True")

Tip for assignment:

x = 1

if isinstance(x, str):
    print("it's a string")
elif isinstance(x, float):
    print("it's a float")
elif isinstance(x, bool):
    print("it's a boolean")
elif isinstance(x, int):
    print("it's an integer")
else:
    print("it's not one of the fourt primive data types")

3.2. Alternative execution

num1 = 5
num2 = 3

if num1 > num2:
    print("num1 is bigger than num2")
else:
    print("num2 is bigger than num1")

3.3. Chained conditions

When there are more than two possibilities, we can use a chained conditional:

num1 = 3
num2 = 3

if num1 > num2:
    print("num1 is bigger than num2")
elif num2 > num1:
    print("num2 is bigger than num1")
elif num1 == num2:
    print("num1 is the same as num2")

3.4. Nested conditional

cond1 = 1 > 0
cond2 = 3 < 4

if cond1:
    print("😖")
    if cond2:
        print("it's break time!!")

When possible, it's better to avoid nested conditionals.

This …

x = 5
if 3 < x < 10:
    print("x is between 3 and 10")

… is better than this:

x = 5

if x > 3:
    if x < 10:
        print("x is between 3 and 10")

You could now already design a simple game!

4. The "in" operator

The "in" operator tests if the value to the left side of the operator is found in a "collection" to the right side of the operator.

var1 = [1,2,"hi",True]

if "hi" in var1:
    print("var1 contains hi")
else:
    print("var1 does not contain hi")