Logical Operators

Logical operators combine two or more relational expressions into a logical expression (compound test). When the operands are booleans, the result is True or False. With non-boolean values, and and or can return one of the original values.

What you'll learn

• Truth tables for and, or, and not
• Short-circuit evaluation
• Why not 10 is False but not 0 is True
• Why 100 and 200 returns 200

The three logical operators

Operator	Purpose
and	True only if both conditions are True
or	True if at least one condition is True
not	Reverses the truth value

1. and operator

Syntax:

RelExpr1 and RelExpr2

Truth table:

Left	Right	Result
True	True	True
True	False	False
False	True	False
False	False	False

Examples:

print(True and False)
print(True and True)

print(10 > 2 and 20 > 4)
print(100 > 200 and 200 > 100)

False
True
True
False

Short-circuit evaluation (and)

Python evaluates from left to right. If the first condition is False, the remaining conditions are skipped.

100 > 200 and 200 > 100

Since 100 > 200 is already False, Python immediately returns False without evaluating 200 > 100.

2. or operator

Syntax:

RelExpr1 or RelExpr2

Truth table:

Left	Right	Result
True	True	True
True	False	True
False	True	True
False	False	False

Examples:

print(True or False)
print(False or False)

print(10 > 2 or 30 > 40)
print(100 > 200 or 40 > 50)

True
False
True
False

Short-circuit evaluation (or)

If the first condition is True, Python skips the rest.

10 > 2 or 30 > 40

The first comparison is already True, so Python never evaluates 30 > 40.

3. not operator

not reverses the truth value.

Value	not
True	False
False	True

Examples:

print(not True)
print(not False)

print(not 10)
print(not 0)

print(not "Python")
print(not "")

False
True
False
True
False
True

not follows the same truthiness rules you learned with bool().

Why 100 and 200 returns 200

This is a common interview question. and and or do not always return booleans — they return one of the operands.

• and returns the first falsy value, otherwise the last value.
• or returns the first truthy value.

print(100 and 200)      # 200
print(0 and 120)        # 0

print(100 or 200)       # 100
print(0 or 200)         # 200

More examples

print(120 and 234 and 450)
print(True and 300)

print("Python" and "Java" and "Data Sci")

450
300
Data Sci

Python keeps evaluating until it finds a falsy value. If none exists, it returns the last operand.

Combined expressions

print(10 and 20 or 30)
print(20 or 30 and 40)

Expression	Output
10 and 20 or 30	20
20 or 30 and 40	20

and has higher precedence than or.

Practice exercises

Exercise 1 — Predict before running:

100 > 200 and 200 > 100

Will Python evaluate the second comparison? (No — short-circuit.)

Exercise 2 — What will these print?

not ""
not "False"

Remember: non-empty strings are truthy.

Exercise 3 — Explain the difference:

100 and 200
100 or 200

Quick knowledge check

1. When does and short-circuit?
   When the first operand is False.

2. What is not 0?
   True

3. What is 100 and 200?
   200 (the last truthy operand)

Summary

• and, or, and not combine logical conditions.
• Short-circuit: and stops on False, or stops on True.
• not reverses truthiness (0, "", and False become True with not).
• With non-boolean values, and and or return one of the operands, not necessarily True or False.

Next lesson: Bitwise Operators — integers bit by bit with <<, >>, &, |, ^, and ~.