Operators

Operators

An operator is a symbol that combines values to produce a new value. You already know + from arithmetic. Python has several families of them, and knowing which family a symbol belongs to tells you what kind of result to expect.

Arithmetic operators

a = 17
b = 5

print(a + b)
print(a / b)
print(a // b)
print(a % b)
print(a ** 2)
print(2 ** 10)

Integer and float division

/ and // are genuinely different operators, and the distinction trips up nearly everyone once.

/ always produces a float, even when the division is exact. 10 / 2 gives 5.0, not 5. If you have come from C, this will surprise you: there, integer division truncates.

// discards the fractional part and gives you the whole-number part of the division. 17 // 5 is 3. With positive numbers you can think of it as "how many times does b fit completely into a".

print(10 / 2)     # 5.0  - a float
print(10 // 2)    # 5    - an int
print(17 / 5)     # 3.4
print(17 // 5)    # 3
print(-17 // 5)   # -4, not -3
print(7.0 // 2)   # 3.0  - float in, float out

Note -17 // 5 giving -4. Floor division rounds down towards negative infinity, not towards zero. This rarely matters in first-year work, but it is worth knowing so the result does not look like a bug.

% gives the remainder, and it is more useful than it first appears:

• n % 2 == 0 tests whether n is even.
• n % 5 == 0 tests divisibility by 5.
• seconds % 60 gives the seconds left over after whole minutes.

total_seconds = 3725

hours = total_seconds // 3600
minutes = (total_seconds % 3600) // 60
seconds = total_seconds % 60

print(f"{hours}h {minutes}m {seconds}s")
print(f"Is 3725 even? {total_seconds % 2 == 0}")

That pairing of // and % — quotient and remainder — is the standard way to split a total into units.

Comparison operators

These compare two values and always produce a boolean, True or False.

marks = 62
pass_mark = 40

print(marks > pass_mark)
print(marks == 62)
print(marks != 62)
print("apple" < "banana")
print(3 == 3.0)

The last two are worth explaining. Strings compare alphabetically by character codes, so "apple" < "banana" is True. And 3 == 3.0 is True because Python compares numeric value, not type, even though type(3) and type(3.0) differ.

Python also allows chained comparisons, which read exactly as they do in mathematics:

marks = 62
print(40 <= marks <= 100)
print(0 < marks < 50)

Logical operators

and, or and not combine boolean values.

• A and B is True only when both are True.
• A or B is True when at least one is True.
• not A flips the value.

attendance = 82
marks = 55

eligible = attendance >= 75 and marks >= 40
print("Eligible:", eligible)

needs_attention = marks < 40 or attendance < 75
print("Needs attention:", needs_attention)

print(not eligible)
print(True and False, True or False, not True)

Python's words and, or, not do the job of &&, || and ! in C and Java. Do not mix them up — && is not valid Python.

These operators short-circuit: in A and B, if A is already False, Python never evaluates B, because the answer cannot change. In A or B, if A is True, B is skipped. This is occasionally useful and occasionally surprising.

Assignment operators

Beyond plain =, there are compound forms that combine an operation with assignment.

score = 10
score += 5     # same as score = score + 5
print(score)

score -= 3
print(score)

score *= 2
print(score)

score //= 4
print(score)

message = "Total"
message += ": 24"
print(message)

+= works on strings too, joining rather than adding. These forms are shorter and make the intent — "update this variable" — clearer than repeating the name.

Precedence

When several operators appear in one expression, Python applies them in a fixed order. From highest priority to lowest:

1. **
2. Unary minus, as in -x
3. *, /, //, %
4. +, -
5. Comparisons: ==, !=, <, >, <=, >=
6. not
7. and
8. or

print(2 + 3 * 4)
print((2 + 3) * 4)
print(2 ** 3 ** 2)
print(10 - 4 - 3)
print(True or False and False)

Two details in there. 2 3 2 gives 512, not 64, because groups right to left: it is 2 (3 ** 2). Everything else at the same level groups left to right, so 10 - 4 - 3 is (10 - 4) - 3.

And True or False and False is True, because and binds tighter than or.

Common mistakes

Using = in a condition. if marks = 40: is a SyntaxError. Comparison needs ==.

Expecting / to give a whole number. total / count gives a float. If you need an integer count of items, use //.

Writing &&, || or ! from C. Python uses and, or, not. if a > 0 && b > 0: is a syntax error.

Comparing a string to a number. "85" > 80 raises TypeError in Python 3, because there is no meaningful ordering between text and numbers. Convert first: int("85") > 80.

Testing float equality directly. 0.1 + 0.2 == 0.3 is False due to binary floating-point representation. Compare with a tolerance instead: abs((0.1 + 0.2) - 0.3) < 0.000001.

Chaining or with values instead of comparisons. if grade == "A" or "B": does not do what it looks like. "B" on its own is a non-empty string, which counts as true, so the condition is always true. Write if grade == "A" or grade == "B":.

Practice

Try the operator exercises on the practice page.