And, Or, Not

Estimated Time: 15 minutes

In Python, you can combine conditions using the logical operators and, or, and not. They let you express more complex conditions, like "even numbers greater than 100" or "the password must be between 8 and 26 characters long, and include a number, a symbol, and a capital and lowercase letter".

Combining Conditions with and and or

To check more than one thing, you can combine conditions with and or or.

if x > 10 and x < 100:
	print("x is a medium sized number")
elif x < 10 or x > 100:
	print("x is either small or large")
else:
	print("x is exactly 10 or 100")

They work basically like they do when you use them in English:

• and is True if both the left and the right side are true, False if either is false
• or is True if either the left or the right side are true, False if both are false

Note: Python’s or results in True if either the left, the right, or both are True. This is somewhat different from how we speak. Sometimes in English, “or” means one or the other, but not both. That’s sometimes called the “exclusive or” or ‘xor’, but it doesn’t have a Python keyword.

Not

Python can turn a boolean into its opposite with not.

not True # False
not False # True
not 100 > 10 # False
not 100 < 10 # True

if not response == "It's awkward":
	print("Stay and par-tay!")

Sometimes it’s useful to be able to express the opposite of a condition.

response = int(input("Enter a big number: "))
if not response > 100:
	print("That's not a big enough number!")

If the input is not greater than 100, it will print output to tell the user that their number isn’t big enough.

not can be combined with other conditions, like and and or. It’s often useful to group expressions with parentheses when making combinations.

if not (x < 10 or x > 100):
	print("x is a medium sized number")

Practice: Print multiples

In this practice, you will write a program that asks the user for a number then prints a statement based on the number the user enters.