Conditional statements and operators

Introduction to Python for Developers

Jasmin Ludolf

Senior Data Science Content Developer

Booleans

# Boolean variable
the_truth = True
print(the_truth)

True

Used to make comparisons

Operators

Comparison operators
- Symbols or combinations of symbols
- Used to compare values
Check if two things are equal
- ==

Checking for equality

# Compare if 2 is equal to 3
2 == 3

False

# Check that 2 is not equal to 3
2 != 3

True

Common use-case: checking login details

Numeric comparison operators

# Is 5 less than 7?
5 < 7

True

# Is 5 less than or equal to 7?
5 <= 7

True

# Is 5 greater than 7?
5 > 7

False

# Is 5 greater or equal to 7?
5 >= 7

False

Other comparisons

# Is James greater than Brian
"James" > "Brian"

True

Strings are evaluated in alphabetical order

Conditional statements

if condition is met, then perform action, otherwise skip

# Check pasta quantities
required_quantity = 500
pasta_quantity = 200


# Compare pasta quantities
if pasta_quantity >= required_quantity

Conditional statements

if condition is met, then perform action, otherwise skip

# Check pasta quantities
required_quantity = 500
pasta_quantity = 200


# Compare pasta quantities
if pasta_quantity >= required_quantity:

Conditional statements

if condition is met, then perform action, otherwise skip

# Check pasta quantities
required_quantity = 500
pasta_quantity = 200


# Compare pasta quantities
if pasta_quantity >= required_quantity:

    print("You have enough pasta!")

Indentation

# Check pasta quantities
required_quantity = 500
pasta_quantity = 200


# Compare pasta quantities
if pasta_quantity >= required_quantity:

print("You have enough pasta!") # This line is not indented

    print("You have enough pasta!")
    ^
IndentationError: expected an indented block

Elif statement

# Check pasta quantities
required_quantity = 500
pasta_quantity = 200

# Compare pasta quantities
if pasta_quantity >= required_quantity:

    print("You have enough pasta!")

elif pasta_quantity >= 300:
    print("Nearly enough pasta. Try a smaller portion.")

Can use as many elif keywords as we like!

Else statement

# Check pasta quantities
required_quantity = 500
pasta_quantity = 200

# Compare pasta quantities
if pasta_quantity >= required_quantity:

    print("You have enough pasta!")

elif pasta_quantity >= 300:
    print("Nearly enough pasta. Try a smaller portion.")

# Otherwise...
else:
    print("Not enough pasta.")

Not enough pasta.

Comparison operators cheat sheet

Operator	Function
`==`	Equal to
`!=`	Not equal to
`>`	More than
`>=`	More than or equal to
`<`	Less than
`<=`	Less than or equal to

Keyword	Function	Use
`if`	If condition is met	First in the workflow
`elif`	Else check if condition is met	After `if`
`else`	Else perform this action	After `elif`

Let's practice!

Introduction to Python for Developers