Learn Logical Operators | Booleans and Comparisons

People say "yes and yes", "yes or no", "definitely not". In Python, the logical operators and, or, and not express these ideas formally and produce Booleans (True/False) you'll use with comparisons in if/while.

What each operator means

Precedence

not binds tighter than and, which binds tighter than or (not > and > or). Use parentheses when in doubt.

For instance, age >= 18 and has_id is True only if both checks succeed:


              123
            
age = 21
has_id = True
print(age >= 18 and has_id)   # True

Truth table

A truth table lists all possible truth values of inputs and shows the resulting output of a logical expression. It's a compact way to reason about logic without running code.

Using the table

If X is False and Y is True, then X and Y is False, X or Y is True, and not X is True.

Return values & short-circuiting (together)

and and or don't always yield the words True/False; they return one of their operands, and Python may stop early once the result is known.

A and B:
- If A is falsey, the whole expression is false and the result is A (Python does not evaluate B);
- If A is truthy, the result depends on B and the expression evaluates to B.
A or B:
- If A is truthy, the expression is true and the result is A (Python does not evaluate B);
- If A is falsey, the result depends on B and the expression evaluates to B.
not X always returns an actual Boolean: True or False.

Q2. Which statement matches classical logic for "neither X nor Y"? A) not X or not Y B) not (X or Y) C) not X and Y D) X and not Y

Q3. What does the expression return?

username = ""
result = username or "Anonymous"

A) "" B) "Anonymous" C) True D) False

Answer key: Q1 → False, False, True; Q2 → B; Q3 → B.


              12345678
            
# Using the returned operand behavior + short-circuiting
print("" or "Guest")      # "Guest"  (left falsey → returns right)
print("User" or "Guest")  # "User"   (left truthy → returns left)

print(0 and 123)          # 0        (left falsey → returns left)
print(5 and 123)          # 123      (left truthy → returns right)

print(not 0, not "hi")    # True False

1. Fill the blanks with `True` or `False`). Let `X = True`, `Y = False`.

2. Which statement matches classical logic for "neither X nor Y"?

3. What does the expression return?

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Section 2. Chapter 4

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What each operator means

Precedence

not binds tighter than and, which binds tighter than or (not > and > or). Use parentheses when in doubt.

For instance, age >= 18 and has_id is True only if both checks succeed:


              123
            
age = 21
has_id = True
print(age >= 18 and has_id)   # True

Truth table

A truth table lists all possible truth values of inputs and shows the resulting output of a logical expression. It's a compact way to reason about logic without running code.

Using the table

If X is False and Y is True, then X and Y is False, X or Y is True, and not X is True.

Return values & short-circuiting (together)

and and or don't always yield the words True/False; they return one of their operands, and Python may stop early once the result is known.

A and B:
- If A is falsey, the whole expression is false and the result is A (Python does not evaluate B);
- If A is truthy, the result depends on B and the expression evaluates to B.
A or B:
- If A is truthy, the expression is true and the result is A (Python does not evaluate B);
- If A is falsey, the result depends on B and the expression evaluates to B.
not X always returns an actual Boolean: True or False.

Q2. Which statement matches classical logic for "neither X nor Y"? A) not X or not Y B) not (X or Y) C) not X and Y D) X and not Y

Q3. What does the expression return?

username = ""
result = username or "Anonymous"

A) "" B) "Anonymous" C) True D) False

Answer key: Q1 → False, False, True; Q2 → B; Q3 → B.


              12345678
            
# Using the returned operand behavior + short-circuiting
print("" or "Guest")      # "Guest"  (left falsey → returns right)
print("User" or "Guest")  # "User"   (left truthy → returns left)

print(0 and 123)          # 0        (left falsey → returns left)
print(5 and 123)          # 123      (left truthy → returns right)

print(not 0, not "hi")    # True False

1. Fill the blanks with `True` or `False`). Let `X = True`, `Y = False`.

2. Which statement matches classical logic for "neither X nor Y"?

3. What does the expression return?

Everything was clear?

Thanks for your feedback!

Section 2. Chapter 4

Logical Operators

What each operator means

Precedence

Truth table

Using the table

Return values & short-circuiting (together)

1. Fill the blanks with True or False). Let X = True, Y = False.

2. Which statement matches classical logic for "neither X nor Y"?

3. What does the expression return?

Awesome!

Logical Operators

What each operator means

Precedence

Truth table

Using the table

Return values & short-circuiting (together)

1. Fill the blanks with True or False). Let X = True, Y = False.

2. Which statement matches classical logic for "neither X nor Y"?

3. What does the expression return?

1. Fill the blanks with `True` or `False`). Let `X = True`, `Y = False`.

1. Fill the blanks with `True` or `False`). Let `X = True`, `Y = False`.