🐍 Python📅 Day 5

Operators in Python

Arithmetic, comparison, logical, assignment, identity and membership operators.

🎯

Learning objectives

→Use arithmetic and comparison operators fluently
→Understand and, or, not vs & | ~
→Apply is vs == correctly

💡 Key points

Two divisions: / gives float, // gives floor int.
** is exponent (2 ** 10 = 1024).
and / or / not are English keywords — not && || ! .
== compares values. is compares identity (same object in memory).
in tests membership: `'a' in 'abc'`, `3 in [1,2,3]`.

💻 Code examples(4)

#1Arithmetic

python

print(7 / 2)     # 3.5   (true division)
print(7 // 2)    # 3     (floor division)
print(7 % 2)     # 1     (modulo)
print(2 ** 10)   # 1024  (power)
print(-7 // 2)   # -4    (floors DOWN, not towards zero!)

// floors towards negative infinity. -7 // 2 = -4, not -3.

#2Comparison + chaining

python

x = 5
print(1 < x < 10)     # True — chained comparison
print(x == 5 != 6)    # True

# equivalent long form:
print(1 < x and x < 10)

Python allows chained comparisons — no need for `and`. Reads like math.

#3Logical operators

python

a, b = True, False
print(a and b)      # False
print(a or b)       # True
print(not a)        # False

# short-circuit + return actual operand
print(0 or "default")   # "default"
print("x" and "y")      # "y"

and/or return one of the operands, not just True/False. Idiom: `name = user_input or 'guest'`.

#4is vs ==

python

a = [1, 2, 3]
b = [1, 2, 3]
c = a

print(a == b)   # True  — same contents
print(a is b)   # False — different objects
print(a is c)   # True  — same object

== checks value equality. is checks identity (memory address). Use `is` only with None: `if x is None:`

🎯 Practice

Q1. What is 5 ** 0.5 ?+

2.23606... (square root of 5). ** works with fractional exponents too.

Q2. Difference between and and & ?+

and is logical (short-circuit, returns operand). & is bitwise (works on integers or NumPy arrays). Don't confuse them.

Q3. How to check if a key exists in a dict?+

if key in my_dict: ... # uses the 'in' membership operator, O(1) for dicts.

📝 Notes

Walrus operator (Python 3.8+)

Assign inside an expression:

if (n := len(data)) > 10:
    print(f"Long input: {n} items")

Handy for while loops that read + test in one line:

while chunk := file.read(1024):
    process(chunk)

Operator precedence — top to bottom

| Level | Operator | |---|---| | Highest | ** | | | unary +x, -x, ~x | | | * / // % | | | + - | | | < <= > >= != == in not in is is not | | | not | | | and | | Lowest | or |

Use parentheses when in doubt.