⚖️ Operators + Boolean Logic

Why it matters

Decision-making and loops rely on booleans. One wrong comparison breaks everything.

The idea

Operators turn expressions into new values. == checks equality of values, is checks identity (same object in memory). For literals, 1 == 1.0 is True but 1 is 1.0 is False.

Arithmetic operators

| Operator | Meaning | | --- | --- | | + | add | | - | subtract | | * | multiply | | / | divide (float) | | // | floor divide | | % | remainder | | ** | power |

/ always returns a float (6 / 2 == 3.0); use // when you want an integer quotient. % gives the remainder — the workhorse of "is this even?" and cyclic-index problems.

Try it

Truthiness in Python: 0, "", [], {}, None are all falsy. Everything else is truthy.

for v in [0, 1, "", "hi", [], [0], None, {}, {"k": 0}]:
  print(repr(v), "->", bool(v))

Short-circuit evaluation: and returns the first falsy operand (or the last value); or returns the first truthy.

print(0 or "fallback")   # 'fallback'
print(5 or "fallback")   # 5
print(0 and "blocked")   # 0
print(5 and "passed")    # 'passed'

Identity vs equality bites in real code:

a = [1, 2, 3]
b = [1, 2, 3]
print(a == b)   # True  — same values
print(a is b)   # False — different objects
c = a
print(a is c)   # True  — same object

Quick check

• Q: When should you use is? A: Identity checks (like x is None).

Mini drills

• Check if a number is even using %.
• Test if a character exists in a string.

Do's and don'ts

• Do use x is None for None checks.
• Don't use is to compare strings or numbers.

Common mistakes

• Mistake: Using is instead of ==. Fix: Use == for value equality.
• Mistake: if x = 3. Fix: Use == in conditions.

Key takeaways

• == compares value; is compares identity.
• Short-circuit operators are useful for defaulting (x or 0).
• Falsy values: 0, "", [], {}, None, set().
• Never compare to True/False explicitly — just use the value.