Comparisons and Logical Operators

Concept: Comparisons and logical operators

A boolean is one of just two values: True or False. Comparisons produce booleans, and booleans drive every decision your program makes.

The two boolean values

is_ready = True
game_over = False

Note the capital letters and no quotes — True is the boolean, "True" is text.

Comparison operators

Each of these asks a question and gives back True or False:

== equal to
!= not equal to
> greater than, < less than
>= greater than or equal to, <= less than or equal to

print(5 == 5)
print(5 != 5)
print(10 >= 20)
print(3 < 7)

Watch out: == compares, = assigns. x = 5 stores 5 in x; x == 5 asks whether x equals 5.

Comparing text

Use == to check whether two strings contain the same text:

name = "Ada"
if name == "Ada":
    print("Welcome back!")
else:
    print("Hello, new visitor!")

The comparison is case-sensitive: "Ada" == "ada" is False. Use = to assign the name, and == to compare it.

Booleans stand on their own

Store a comparison in a variable, and that variable goes straight into an if — you never need to write == True:

score = 25
banked = score >= 20
print(banked)
if banked:
    print("done for this round")

banked holds True, so the if runs.

Your turn

Add two lines: print whether score is at least 20, then print whether it is not equal to 0.

score = 18
# add two prints: one comparison each

Expected output

False
True

Combine comparisons with and, or and not

and is true when both conditions are true.
or is true when at least one condition is true.
not reverses a condition's truth value.

These descriptions apply to Boolean conditions. Python can also use and and or with other values, but that is beyond this introduction.

score = 25
attempts_left = 2
print(score >= 20 and attempts_left > 0)
print(score >= 30 or attempts_left > 0)
print(not (score >= 20))

The results are True, True, then False. Parentheses make grouping clear when combining several conditions.

Write a complete comparison on each side

To accept either 1 or 2, write choice == 1 or choice == 2. Writing choice == 1 or 2 does not repeat the comparison: the non-zero number 2 makes that condition truthy regardless of choice.

Python uses the words and, or, not, rather than && or ||. For a value inside a range, both boundaries must hold: age >= 12 and age <= 18.

Your turn: combine two questions

Print whether the player has at least 20 points and at least one attempt left.

score = 25
attempts_left = 2
# Print one combined comparison.

Expected output

True

See also: if, elif, else, Data Validation.

Practise this in the free Python course, where every exercise checks your code instantly.