4.1 Boolean values

Boolean values are the backbone of decision-making in programming. They represent true or false states, allowing programs to make choices based on conditions. This fundamental concept enables developers to create dynamic, responsive code that adapts to different scenarios.

Comparison operators and logical operators work hand-in-hand with Boolean values. These tools let programmers craft complex conditions, evaluate data, and control program flow. Understanding how to use and manipulate Boolean values is key to writing efficient, logical code.

Boolean Values and Logic

Boolean values in programming decisions

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• Boolean values represent the truth values of logic and Boolean algebra with two possible values:

  True

  and

  False

• Used to make decisions and control the flow of a program by determining which code block to execute in conditional statements (

  [if](https://www.fiveableKeyTerm:If)

  ,

  [elif](https://www.fiveableKeyTerm:elif)

  ,

  [else](https://www.fiveableKeyTerm:Else)

  )
• Boolean expressions evaluate to either

  True

  or

  False

  using comparison operators (==, !=, <, >, <=, >=) and logical operators (and, or, not)
• Enable programs to make decisions based on conditions and execute different code paths accordingly (authentication, input validation)

Storage of true/false states

• Boolean variables can store either

  True

  or

  False

  and are declared using the

  [bool](https://www.fiveableKeyTerm:bool)

  data type in Python
• Useful for keeping track of conditions or states in a program such as

  is_logged_in = True

  to indicate that a user is logged in
• Boolean variables can be updated throughout the program based on certain conditions or user actions

  • is_valid = True

    if user input meets validation criteria, otherwise

    is_valid = False

  • game_over = True

    when the player's health reaches zero or they complete the final level

Comparison operators for conditions

• Comparison operators compare values and return a Boolean result

  • ==

    (equal to),

    !=

    (not equal to),

    <

    (less than),

    >

    (greater than),

    <=

    (less than or equal to),

    >=

    (greater than or equal to)
• Can be used with various data types
  1. Numbers (integers and floats):

     5 > 3

     ,

     2.5 <= 2.7

  2. Strings:

     "hello" == "hello"

     ,

     "apple" != "banana"

  3. Booleans:

     True == True

     ,

     False != True

• Comparison operators are often used in conditional statements to make decisions based on the comparison result

  • if score >= 60: print("Pass")

    to check if a student's score is greater than or equal to the passing threshold

  • if username == "admin" and password == "secret": grant_access()

    to authenticate a user's credentials

Boolean conversion with data types

• Boolean values can be converted to other data types using type conversion functions

  • [int](https://www.fiveableKeyTerm:int)(True)

    returns

    1

    ,

    int(False)

    returns

    0

  • [float](https://www.fiveableKeyTerm:Float)(True)

    returns

    1.0

    ,

    float(False)

    returns

    0.0

  • [str](https://www.fiveableKeyTerm:str)(True)

    returns

    "True"

    ,

    str(False)

    returns

    "False"

• Other data types can be converted to Boolean values using the

  [bool()](https://www.fiveableKeyTerm:bool())

  function
  • Falsy values like

    bool(0)

    ,

    bool(0.0)

    ,

    bool("")

    ,

    bool([])

    ,

    bool({})

    , and

    bool(None)

    return

    False

  • Any non-zero number, non-empty string, non-empty list, non-empty dictionary, or any other object returns

    True

• Useful for checking the truthiness of values and making decisions based on their Boolean equivalent

  • if bool(username): ...

    to check if the username is not an empty string

  • if bool(items): ...

    to check if a list or dictionary has any elements

Boolean logic in conditionals

• Boolean logic operators (logical operators such as

  and

  ,

  or

  ,

  not

  ) are used to combine or negate Boolean values

  • and

    returns

    True

    if both operands are

    True

    , otherwise

    False

  • or

    returns

    True

    if at least one operand is

    True

    , otherwise

    False

  • not

    returns the opposite Boolean value of its operand
• Boolean logic is used in conditional statements to create more complex conditions

  • if age >= 18 and is_student: apply_discount()

    to check if a customer is both an adult and a student to apply a discount

  • if not is_valid: display_error_message()

    to execute code when a condition is not met
• Boolean expressions can be grouped using parentheses to control the order of evaluation

  • if (x > 0) or (y < 0 and z == 0): handle_special_case()

    to prioritize the evaluation of certain conditions over others