Python Comparison and Logic

Asking the computer questions

Programs constantly need to make decisions. Is the player out of lives? Is the password correct? Is the temperature too high? Before a program can decide anything, it has to ask a question and get a yes-or-no answer. In Python those answers are called booleans, and the questions are built from comparison and logic operators.

This is the engine behind the conditionals in Python you may have already seen with if. Here we'll look closely at how the conditions themselves work.

True and False: the booleans

A boolean is a value that is either True or False. Those two words are special in Python and must always start with a capital letter.

is_raining = True
is_sunny = False

print(is_raining)        # True
print(type(is_raining))  # <class 'bool'>

• is_raining = True stores the boolean True in a variable.
• type(is_raining) confirms its type is bool, short for boolean.

Booleans are the simplest type in Python — only two possible values — but they're the foundation of every decision your program makes.

Comparison operators

A comparison checks how two values relate, and the result is always a boolean. Here are the six comparisons:

print(5 == 5)   # True   equal to
print(5 != 3)   # True   not equal to
print(5 > 3)    # True   greater than
print(5 < 3)    # False  less than
print(5 >= 5)   # True   greater than or equal to
print(3 <= 2)   # False  less than or equal to

Reading these:

• == asks "are these equal?" — 5 == 5 is True.
• != asks "are these different?" — 5 != 3 is True because they are.
• >, <, >= and <= compare sizes, just like in maths.

The most important point: == is a question, = is a command. A single = stores a value (x = 5), while a double == checks equality (x == 5). Mixing them up is the classic beginner bug.

Comparisons work on text too, checking whether strings match exactly:

password = "open123"
print(password == "open123")  # True
print(password == "Open123")  # False  (capital O is different)

String comparison is case-sensitive, so "open123" and "Open123" are not equal.

Combining conditions with and, or, not

Often a single comparison isn't enough. You might need two things to be true at once, or either of two things. Python gives you three logical operators: and, or, and not.

and is True only when both sides are True:

age = 15
print(age > 12 and age < 18)   # True
print(age > 12 and age < 14)   # False

• age > 12 is True and age < 18 is True, so the whole thing is True.
• In the second line, age < 14 is False, and because and needs both sides, the result is False.

or is True when at least one side is True:

day = "Saturday"
print(day == "Saturday" or day == "Sunday")  # True
print(day == "Monday" or day == "Sunday")    # False

• The first line is True because the left side matches.
• The second line is False because neither side is True.

not flips a boolean to its opposite:

print(not True)        # False
print(not (5 > 3))     # False, because 5 > 3 is True
print(not (5 < 3))     # True, because 5 < 3 is False

A simple way to remember it: and is strict (everything must be true), or is generous (one is enough), and not is the opposite-switch.

Putting it inside an if statement

These boolean expressions are exactly what if statements check:

temperature = 30

if temperature > 25 and temperature < 35:
    print("Warm but comfortable")
else:
    print("Outside the comfort zone")

• The condition temperature > 25 and temperature < 35 becomes True, so the first branch runs and prints Warm but comfortable.
• If the temperature were 40, the condition would be False and the else branch would run instead.

Worked example: a login check

Let's build a small login checker that requires the right username and the right password.

correct_user = "ada"
correct_pass = "lovelace"

username = "ada"
password = "lovelace"

logged_in = (username == correct_user) and (password == correct_pass)

if logged_in:
    print("Welcome, " + username + "!")
else:
    print("Login failed.")

How it works:

1. username == correct_user checks the name and produces a boolean. password == correct_pass checks the password and produces another.
2. The and combines them: logged_in is only True if both match. If either is wrong, logged_in is False.
3. The if logged_in: line then uses that boolean to decide which message to print.

Try changing the password to "wrong". Now the second comparison is False, the and makes logged_in False, and the program prints Login failed. — exactly the safe behaviour you'd want.

Try it yourself

Write a program that decides whether someone can ride a rollercoaster. The rule is: you must be at least 12 years old AND at least 140 cm tall.

• Create two variables, age and height.
• Build one boolean: can_ride = age >= 12 and height >= 140.
• Use an if to print either "You can ride!" or "Sorry, not yet.".

Then test it with different values: a tall 10-year-old, a short 14-year-old, and a 13-year-old who is 145 cm. Only the last one should pass. When you're confident, revisit conditionals in Python to combine these conditions with elif for even smarter decisions.