Python Operators

Operators are symbols that tell Python to perform a specific computation or comparison on one or more values. Python groups operators into families — arithmetic, comparison, and logical — and each family has its own rules and behaviors that are important to get exactly right.

One area where Python differs noticeably from many other languages is division: Python has two distinct division operators, one that always returns a float-style result and one that always rounds down to a whole number, and mixing them up is a very common source of bugs.

Why it matters

Operators are how conditions and calculations are written, and a few of Python's behave differently from other languages: and and or are words, comparisons can be chained, and is is not the same as ==. Mixing up the last pair is a classic bug that works in testing and fails later.

Arithmetic Operators

Python supports the standard arithmetic operators: + (addition), - (subtraction), * (multiplication), / (true division, always returns a float), // (floor division, rounds down to the nearest whole number), % (modulus, the remainder after division), and ** (exponentiation, e.g. 2 ** 3 is 8). Floor division and modulus both follow the sign of the divisor, which can produce results that surprise programmers coming from other languages when negative numbers are involved.

Comparison Operators

Comparison operators — == != > < >= <=</code> — compare two values and always produce a bool (True or False). == checks for equality of value, not identity; to check whether two names refer to the literally same object in memory, Python provides a separate keyword, is.

Logical Operators

Python spells out its logical operators as words rather than symbols: and, or, and not. Like most languages, and and or short-circuit — Python stops evaluating as soon as the overall result is determined, which matters when the right-hand expression has a side effect or could raise an error.

Examples

print(7 / 2)     # true division, always float
print(7 // 2)    # floor division, rounds down
print(7 % 2)     # modulus/remainder
print(2 ** 5)    # exponentiation
print(-7 // 2)   # floor division rounds toward negative infinity
print(-7 % 2)    # follows the sign of the divisor

3.5
3
1
32
-4
1

age = 20
has_id = False

print(age >= 18 and has_id)
print(age >= 18 or has_id)
print(not has_id)

# Python allows chained comparisons
print(1 < age < 65)

False
True
True
True

Exercise

Write a function that returns True for a leap year. A year is a leap year if it is divisible by 4, except that years divisible by 100 are leap years only if they are also divisible by 400.

Expected output: True, False, True (one per line)

def is_leap(year):
    # TODO: return True if the year is a leap year
    pass


print(is_leap(2024))
print(is_leap(1900))
print(is_leap(2000))

def is_leap(year):
    return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)


print(is_leap(2024))
print(is_leap(1900))
print(is_leap(2000))

Quick quiz

Interview questions