Logical Operators: or

The second logical operator is or. “If it's Saturday or Sunday, it's the weekend”:

day = "Sunday"
if day == "Saturday" or day == "Sunday":
    print("It's the weekend")

This prints:

It's the weekend

A condition joined with or is true if at least one of its parts is true. It's false only if all the parts are false:

• True or True is True
• True or False is True
• False or True is True
• False or False is False

A typical mistake is to shorten the condition the way we speak: day == "Saturday" or "Sunday". Python takes the right part on its own: it's just the text "Sunday", not a comparison. Text that isn't empty counts as true, so the whole condition is always true, even on Monday. Each part needs its own comparison: day == "Saturday" or day == "Sunday".

You can use and and or in one condition. Just as multiplication goes before addition, and goes before or. Use parentheses to group what belongs together, as in math:

day = "Saturday"
temperature = 15
if (day == "Saturday" or day == "Sunday") and temperature > 20:
    print("Let's go on a trip")
else:
    print("Let's stay at home")

This prints:

Let's stay at home

The part in parentheses is evaluated first: it's Saturday, so it's true. But temperature > 20 is false, and True and False is false. Without the parentheses, Python would first join day == "Sunday" and temperature > 20, and the condition would be true on every Saturday, whatever the weather.