Boolean Logic

Boolean logic is the foundation of decision-making in Python. It involves expressions that evaluate to either True or False, and it’s commonly used in conditional statements and loops.

Boolean Values

Python has two Boolean values: True and False.

Examples:

print(True)   # True
print(False)  # False
print(type(True))  # <class 'bool'>

Comparison Operators

Comparison operators are used to compare values, returning True or False.

Examples:

x = 10
y = 20

print(x == y)  # False
print(x < y)   # True
print(x >= 10) # True

Logical Operators

Logical operators combine multiple conditions.

Examples:

# and operator
print((5 > 3) and (10 > 7))  # True
print((5 > 3) and (10 < 7))  # False

# or operator
print((5 > 3) or (10 < 7))   # True
print((5 < 3) or (10 < 7))   # False

# not operator
print(not (5 > 3))           # False

Truthy and Falsy Values

In Python, some values are considered truthy or falsy when evaluated in a Boolean context:

• Falsy Values: None, False, 0, 0.0, "" (empty string), [] (empty list), {} (empty dictionary).
• Truthy Values: Most other values.

Examples:

print(bool(0))        # False
print(bool(""))       # False
print(bool(123))      # True
print(bool("Python")) # True

Short-Circuit Evaluation

Logical operators use short-circuit evaluation, meaning Python stops evaluating as soon as the result is determined.

Examples:

x = 10

# Short-circuit with 'or'
print((x > 5) or (x / 0))  # True (no error because the first condition is True)

# Short-circuit with 'and'
print((x > 15) and (x / 0))  # False (no error because the first condition is False)

Common Use Cases

1. Validating Input:

   age = int(input("Enter your age: "))
   if age > 0 and age < 120:
       print("Valid age")
   else:
       print("Invalid age")
   

2. Combining Conditions:

   score = 85
   if score >= 90 or (score >= 80 and score < 90):
       print("You passed!")
   

3. Negation:

   is_logged_in = False
   if not is_logged_in:
       print("Please log in.")
   

Practice Exercises

1. Write a program that:
   • Asks the user for a number.
   • Prints whether the number is positive, negative, or zero.
2. Create a program to:
   • Check if a string entered by the user is empty or not.
3. Write a program that:
   • Asks for two numbers.
   • Prints True if both numbers are greater than 10; otherwise, prints False.

Boolean logic is at the heart of decision-making in Python and is essential for creating dynamic and interactive programs!