2.1 Relational and Logical Operators

Programs do not only run statements in order. They often need to check whether a condition is true, then choose what to do next. A condition usually produces a Boolean value: True or False.

Relational operators

Relational operators compare two values. The result of a comparison is a Boolean value, not another number.

Common Python relational operators:

• <: less than
• >: greater than
• <=: less than or equal to
• >=: greater than or equal to
• ==: equal to
• !=: not equal to

Important: one equals sign = means assignment. Two equals signs == mean comparison.

age = 17

print(age < 18)      # True
print(age == 18)     # False
print(age != 18)     # True

age = 17 stores 17 in the variable age. age == 18 checks whether the current value of age equals 18.

Logical operators

Logical operators combine multiple conditions. Their result is still a Boolean value.

• and: the whole expression is True only when every condition is True.
• or: the whole expression is True when at least one condition is True.
• not: turns True into False, and False into True.

age = 20
has_ticket = True

print(age >= 18 and has_ticket)    # True
print(age < 18 or has_ticket)      # True
print(not has_ticket)              # False

It helps to read conditions like plain language: age >= 18 and has_ticket means “the age is at least 18, and the person has a ticket.”

Combining conditions

Python supports chained comparisons:

age = 16
print(0 < age < 18)    # True

This is equivalent to:

print(0 < age and age < 18)

When a condition becomes complex, use parentheses or meaningful variable names to keep the logic readable.

score = 85
attendance = 92

passed = score >= 60 and attendance >= 80
excellent = score >= 90 or attendance >= 95

print(passed)       # True
print(excellent)    # False

Do not rush to squeeze every condition into one line. Naming smaller conditions makes the program easier to read and debug.