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.


              1234567891011121314151617
            
# Choosing a display name for a user profile
username = ""             # user didn't set a custom name
print(username or "Guest")   # "Guest" → fallback to default name

username = "Alice"
print(username or "Guest")   # "Alice" → custom name is used

# Checking login attempts and access permissions
login_attempts = 0
access_level = 123
print(login_attempts and access_level)  # 0 → login not yet attempted

login_attempts = 5
print(login_attempts and access_level)  # 123 → user has access after attempts

# Checking empty and non-empty values
print(not 0, not "Hello")  # True False → 0 is falsey, non-empty string is truthy

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.


              1234567891011121314151617
            
# Choosing a display name for a user profile
username = ""             # user didn't set a custom name
print(username or "Guest")   # "Guest" → fallback to default name

username = "Alice"
print(username or "Guest")   # "Alice" → custom name is used

# Checking login attempts and access permissions
login_attempts = 0
access_level = 123
print(login_attempts and access_level)  # 0 → login not yet attempted

login_attempts = 5
print(login_attempts and access_level)  # 123 → user has access after attempts

# Checking empty and non-empty values
print(not 0, not "Hello")  # True False → 0 is falsey, non-empty string is truthy

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`.