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27. Booleans and Logic

1. Introduction​

A boolean is a data type with only two possible values: True or False.
Booleans are the foundation of decision-making in programming.

In Python, booleans often appear as the result of comparisons or logical operations.

2. Boolean Values​

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

3. Comparisons that Return Booleans​

print(5 > 3)   # True
print(10 == 2) # False
print(7 <= 7)  # True

4. The bool() Function​

Any value can be converted to a boolean using bool().

  • Falsy values (evaluated as False):

    • 0, 0.0
    • "" (empty string)
    • [], {}, () (empty collections)
    • None
    • False

  • Everything else is True.

Examples:

print(bool(0))       # False
print(bool(""))      # False
print(bool("hi"))    # True
print(bool([1, 2]))  # True

5. Logical Operators​

Logical operators combine boolean values.

a = True
b = False

print(a and b)  # False
print(a or b)   # True
print(not a)    # False

6. Combining Comparisons​

You can use logical operators with comparisons:

x = 10
print(x > 5 and x < 20)   # True
print(x < 5 or x == 10)   # True
print(not(x == 10))       # False

7. Operator Precedence with Booleans​

Order of evaluation:

  1. not
  2. and
  3. or

Example:

print(True or False and False)   # True (and is evaluated first)

8. Identity and Membership in Boolean Contexts​

fruits = ["apple", "banana"]

print("apple" in fruits)     # True
print("cherry" not in fruits) # True

a = [1, 2, 3]
b = a
c = [1, 2, 3]

print(a is b)  # True
print(a is c)  # False

9. Practical Examples​

age = 18
has_id = True

if age >= 18 and has_id:
    print("Access granted")
else:
    print("Access denied")

10. Next Steps​

✅ You now understand booleans, comparisons, and logical operators.
In the next chapter, we’ll explore if statements, the first step into control flow.