Understanding and Creating Boolean Expressions

Boolean expressions are the building blocks of decision-making in programming. They evaluate to either true or false, allowing your code to make choices and control the flow of execution.

Boolean Operators

At the core of boolean expressions are boolean operators:

• and: Returns true only if both operands are true. true and true -> true true and false -> false false and true -> false false and false -> false
• or: Returns true if at least one operand is true. true or true -> true true or false -> true false or true -> true false or false -> false
• not: Negates the truth value of its operand. not true -> false not false -> true

Comparison Operators

You often use comparison operators to compare values and generate boolean results:

• ==: Equal to.
• !=: Not equal to.
• >: Greater than.
• <: Less than.
• >=: Greater than or equal to.
• <=: Less than or equal to.

Building Boolean Expressions

Boolean expressions can be combined using parentheses to control order of operations and create complex logic:

(a > 10) and (b < 5) or (c == 0)

This expression checks if:

1. a is greater than 10, and
2. b is less than 5, or
3. c is equal to 0.

The entire expression will evaluate to true if at least one of the conditions is met.

Example: Checking for a Valid Password

password = input("Enter your password: ")

if len(password) >= 8 and any(char.isdigit() for char in password) and any(char.isupper() for char in password):
    print("Valid password!")
else:
    print("Invalid password. Password must be at least 8 characters long, contain at least one number, and at least one uppercase letter.")

This code checks if a user-entered password meets the following criteria:

• At least 8 characters long
• Contains at least one digit
• Contains at least one uppercase letter

The if statement uses a boolean expression to determine if the password is valid.

Summary

Boolean expressions are essential for writing programs that make decisions and control flow. Mastering boolean operators and comparison operators allows you to create complex logic that can handle various scenarios in your code.