~/Python Operators

10.1 The Seven Families of Operators

10.2 Arithmetic Operators

Seven symbols — the usual four from school plus three extras that Python borrows from mathematics.

a, b = 13, 4
print(a + b, a - b, a * b)        # 17 9 52
print(a / b)                       # 3.25   — always a float
print(a // b)                      # 3      — quotient (floor)
print(a % b)                       # 1      — remainder
print(a ** b)                      # 28561  — 13⁴
print(-a)                          # -13    — unary minus

print(10 / 2)      # 5.0     (float)
print(10 // 2)     # 5       (int)
print(-7 // 2)     # -4      (floor division rounds TOWARDS NEGATIVE INFINITY)

10.3 Relational (Comparison) Operators

Compare two values and produce a Boolean — either True or False.

marks = 72
print(marks >= 33)           # True  — pass
print(marks == 100)          # False
print("abc" < "abd")          # True  — strings compare dictionary-order
print([1, 2] == [1, 2])       # True  — lists compare element-wise

age = 16
print(13 <= age < 20)      # True  — means "13 ≤ age AND age < 20"

10.4 Logical Operators

Combine Boolean values. Python uses the English keywords and, or, not — not the C-style &&, ||, !.

age    = 17
has_id = True

# Is this person allowed to vote AND does she carry ID?
print(age >= 18 and has_id)     # False  — age is 17
print(age >= 18 or  has_id)     # True   — one branch holds
print(not has_id)                # False

10.5 Assignment Operator — =

A single = binds a name (L-value) to a value (R-value). Python also allows two neat shortcuts:

x, y = 10, 20
print(x, y)        # 10 20
x, y = y, x
print(x, y)        # 20 10   — swap in one line

10.6 Augmented Assignment Operators

A compact way of saying "take the current value, apply an arithmetic operation, store back". Every arithmetic operator has an augmented form.

total = 0
for marks in [85, 72, 91]:
    total += marks           # same as total = total + marks
print(total)                 # 248

count = 1
count *= 2                     # 2
count **= 3                    # 8   (2 ** 3)

10.7 Identity Operators — is & is not

Identity operators ask: "Are the two names pointing to the same object in memory?" — not whether the values happen to be equal.

a = [1, 2, 3]
b = [1, 2, 3]       # equal in value, but a fresh object
c = a                   # c is the same object as a (alias)

print(a == b)             # True   — values match
print(a is b)             # False  — different objects in memory
print(a is c)             # True   — same object
print(a is not b)         # True

if result is None:   # ✓ the idiomatic way
    ...
if x is 1000:         # ❌ unreliable — do not rely on int identity
    ...

10.8 Membership Operators — in & not in

Ask whether a value appears inside a sequence or collection — a string, list, tuple, dictionary (its keys), or any iterable. Returns a Boolean.

vowels = "aeiou"
print("e" in vowels)            # True
print("z" not in vowels)        # True

marks = [85, 72, 91, 68]
print(72 in marks)              # True
print(100 not in marks)          # True

student = {"name": "Aarav", "roll": 22}
print("name" in student)        # True   — checks KEYS of a dict
print("Aarav" in student)       # False  — not a key

choice = input("y/n? ").lower()
if choice in ("y", "yes"):
    print("Confirmed")
elif choice in ("n", "no"):
    print("Cancelled")
else:
    print("Please type y or n")

10.9 The Whole Menu — One-page Cheat Sheet

10.9.1 Operator Precedence (preview)

When several operators appear in one expression, Python evaluates them in a fixed order. A detailed table is covered in Chapter 11 — Expressions, but here is the rough picture, highest precedence first:

print(2 + 3 * 4)            # 14  (not 20)
print((2 + 3) * 4)          # 20