or in Python: Logical OR Operator Explained

The Python or operator is a logical operator that returns True if at least one of the operands evaluates to True. It's a binary operator typed as plain English word "or" and is used to create compound Boolean expressions in conditional statements, loops, and function logic.

Basic or Operator Syntax

The or operator takes two operands and evaluates whether at least one is true.

condition1 or condition2

The or operator returns True when at least one operand is True. It only returns False when both operands are False.

Example 1: Basic Boolean Expression

bool1 = 2 > 3  # False
bool2 = 2 < 3  # True

result = bool1 or bool2
print(result)

True

Example 2: Both False

bool1 = 2 > 3  # False
bool2 = 5 > 10  # False

result = bool1 or bool2
print(result)

False

When both conditions are False, the or operator returns False.

Truth Table for or Operator

Understanding how the or operator works with different boolean combinations is essential.

The or operator returns True when at least one operand is True.

Example: All Truth Table Cases

# Case 1: True or True = True
if True or True:
    print("Case 1: True")  # This executes

# Case 2: True or False = True
if True or False:
    print("Case 2: True")  # This executes

# Case 3: False or True = True
if False or True:
    print("Case 3: True")  # This executes

# Case 4: False or False = False
if False or False:
    print("Case 4: True")
else:
    print("Case 4: False")  # This executes

Case 1: True
Case 2: True
Case 3: True
Case 4: False

How OR Works with Non-Boolean Values

Python's or operator returns the first object that evaluates to true, or the last object if all are false.

Example: OR with Different Data Types

# Returns first truthy value or last value
print(2 or 3)        # Output: 2
print(5 or 0.0)      # Output: 5
print([] or 3)       # Output: 3
print(0 or {})       # Output: {}
print('' or 'Hello') # Output: Hello

2
5
3
{}
Hello

The or operator returns the first truthy value, or the last value if all are falsy.

Falsy values (evaluated as False):

• False
• None
• 0, 0.0
• Empty string ''
• Empty list []
• Empty dict {}
• Empty tuple ()

Truthy values (evaluated as True):

• Non-zero numbers (positive or negative)
• Non-empty strings
• Non-empty collections
• True

Short-Circuit Evaluation

The or operator uses short-circuit evaluation, stopping as soon as it finds a truthy value and not evaluating remaining operands.

Example: Demonstrating Short-Circuit

def true_func():
    print("First function called")
    return True

def false_func():
    print("Second function called")
    return False

# Second function never executes
result = true_func() or false_func()
print(result)

First function called
True

Notice that "Second function called" never prints because true_func() returned True, so Python skipped evaluating false_func(). This optimization improves performance and prevents unnecessary computations.

Using OR in Conditional Statements

The or operator is commonly used in if statements to check multiple conditions.

Example 1: OR with If Statements

def check_number(a):
    if a % 5 == 0 or a % 3 == 0:
        print(f"{a} is a multiple of 3 or 5")
    else:
        print(f"{a} is not a multiple of 3 or 5")

check_number(10)  # Output: 10 is a multiple of 3 or 5
check_number(22)  # Output: 22 is not a multiple of 3 or 5
check_number(9)   # Output: 9 is a multiple of 3 or 5

10 is a multiple of 3 or 5

Example 2: Multiple Valid Inputs

def answer():
    ans = 'yes'  # Simulating user input
    if ans.lower() == 'yes' or ans.lower() == 'y':
        print(f'Positive answer: {ans}')
    elif ans.lower() == 'no' or ans.lower() == 'n':
        print(f'Negative answer: {ans}')
    else:
        print('Invalid input')

answer()

Positive answer: yes

This pattern allows checking multiple valid inputs for the same condition.

Chaining Multiple OR Operations

You can chain multiple or operators together to check if a variable matches any value.

Example 1: Chaining OR Operators

# Check if variable matches any value
user_role = 'admin'

if user_role == 'admin' or user_role == 'moderator' or user_role == 'editor':
    print('Access granted')
else:
    print('Access denied')

Access granted

Example 2: Better Alternative Using 'in'

# Better alternative using 'in' operator
user_role = 'admin'

if user_role in ['admin', 'moderator', 'editor']:
    print('Access granted')
else:
    print('Access denied')

Access granted

Using the in operator is often more readable when checking membership in multiple values.

OR vs Bitwise OR (|)

The logical or operator works with boolean expressions, while the bitwise | operator performs bit-level operations on integers.

Logical OR:

# Logical OR
a = True or False
print(a)

True

Bitwise OR (works with integers):

# Bitwise OR (works with integers)
x = 10  # Binary: 1010
y = 4   # Binary: 0100
result = x | y  # Binary: 1110
print(result)

14

Common Use Cases

Use Case 1: Input Validation

def validate_age(age):
    if age < 0 or age > 150:
        return "Invalid age"
    return "Valid age"

print(validate_age(25))   # Output: Valid age
print(validate_age(-5))   # Output: Invalid age
print(validate_age(200))  # Output: Invalid age

Valid age

Use Case 2: Default Values

def greet(name):
    # Use default if name is empty or None
    display_name = name or "Guest"
    print(f"Hello, {display_name}!")

greet("Alice")  # Output: Hello, Alice!
greet("")       # Output: Hello, Guest!
greet(None)     # Output: Hello, Guest!

Hello, Alice!
Hello, Guest!
Hello, Guest!

Use Case 3: Permission Checking

def can_access_resource(user):
    has_subscription = user.get('subscription', False)
    is_admin = user.get('admin', False)
    
    if has_subscription or is_admin:
        return "Access granted"
    return "Access denied"

user1 = {'name': 'John', 'subscription': True}
user2 = {'name': 'Jane', 'admin': True}
user3 = {'name': 'Bob'}

print(can_access_resource(user1))  # Access granted
print(can_access_resource(user2))  # Access granted
print(can_access_resource(user3))  # Access denied

Access granted
Access granted
Access denied

Common Mistakes to Avoid

Mistake 1: Confusing OR with AND

x = 5

# Wrong: This doesn't work as intended
# if x == 3 or 4 or 5:  # Always True because 4 and 5 are truthy
#     print("Match")

# Correct
if x == 3 or x == 4 or x == 5:
    print("Match")

# Better
if x in [3, 4, 5]:
    print("Match")

Mistake 2: Expecting Boolean Return

# OR doesn't always return boolean
result = 0 or []
print(result)        # Output: [] (not False)
print(type(result))  # Output: 

# Use bool() for explicit boolean
result = bool(0 or [])
print(result)        # Output: False

Best Practices

Practice 1: Use 'in' Operator When Checking Membership

# Less readable
if user_role == 'admin' or user_role == 'moderator' or user_role == 'editor':
    print('Access granted')

# More readable - prefer 'in' operator
if user_role in ['admin', 'moderator', 'editor']:
    print('Access granted')

Prefer <code>in</code> operator when checking membership in multiple values

Practice 2: Leverage Short-Circuit Evaluation

# Put the most likely to be True condition first
def quick_check():
    return True

def slow_operation():
    return False

if quick_check() or slow_operation():
    print("At least one is True")

Use short-circuit evaluation for performance optimization

Practice 3: Use Parentheses for Complex Conditions

# Less readable
if age >= 18 and has_license or is_supervised and age >= 16:
    allow_driving()

# More readable with parentheses
if (age >= 18 and has_license) or (is_supervised and age >= 16):
    allow_driving()

Use parentheses for complex conditions to improve readability

Practice 4: Avoid Mixing Logical and Bitwise Operators

# Clear intent
if (x > 0 or y > 0):
    print("At least one is positive")

# Avoid confusion
# if x > 0 | y > 0:  # This is bitwise OR, not logical OR!

Avoid mixing logical and bitwise operators without clear intent

Related Topics

• if in python - Learn about basic conditional statements
• if else in python - Learn how to handle alternative conditions
• and in python - Combine multiple conditions
• not in python - Negate conditions with NOT operator
• is in python - Check object identity
• in in python - Check membership in sequences

Frequently Asked Questions