Kevin C. Tofel

02 - Boolean Logic and Numeric Operators

Boolean Logic and Numeric Operators

Primary operators are Not, And and Or.

Not inverts a Boolean value. And returns true if and only if all conditions are true, allowing you to check for multiple conditions. Or returns true if and only if at least one condition is true.

Using these operators, you can, for example:

  • Combine multiple conditions
  • Manage user access
  • Enable or disable certain app features based on configuration.

Precedent order for Boolean functions is: Not, And, Or.

Common examples of Boolean values:

bool(0)        # False
bool(1)        # True
bool("")       # False
bool("0")      # True
bool([])       # False
bool([0])      # True

Boolean expressions

Example:

age = 25
has_id = True

# Both conditions must be True
can_enter = age >= 21 and has_id  # Evaluates to True

# Only one condition needs to be True
is_weekend = False
is_holiday = True
stay_home = is_weekend or is_holiday  # Evaluates to True

# Flips the result
print(not is_weekend)  # Evaluates to True

Nested Boolean expressions

Example:

# Variables representing a user's status
is_admin = False
has_premium_pass = True
is_vip = False
has_ticket = True

# Nested boolean expression
# The user can enter if they are an admin OR if they have a valid combination of VIP/Ticket features.
can_enter = is_admin or ((has_premium_pass or is_vip) and has_ticket)

print(can_enter)  # Output: True

Useful for checking multiple conditions.

Relational Operators

Compare values and return True or False

Equal to (==)

  • Checks if two values are the same. Example: a == b returns true if both hold similar values. Do not confuse this with the assignment (=) operator. = is used to assign a value. == is used to check for equality.
  • Not Equal to (!=) Verifies if two values differ. Example: a != b is true if a and b are distinct.
  • Greater Than (>) Determines if the value on the left is larger. Example: a > b indicates true if a exceeds b.
  • Greater Than or Equal to (>=) Checks if the left side value is not less. Example: a >= b is true if a is greater or equal to b.
  • Less Than (<) Evaluates if the left value is smaller. Example: a < b gives true if a is less than b.
  • Less Than or Equal to (<=) Confirms if the left-side value is not greater. Example: a <= b holds true if a is less than or equal to b.

Floating Point Accuracy

Since Python stores numbers as representations of binary values, high precision can lead to small approxmiations. As a result, using numeric operators can return unxpected values. Most decimal fractions (such as 0.1) cannot be represented exactly in binary floating-point, so Python stores the closest representable value.

Example: 0.1 + 0.2 != 0.3 It actually equals 0.3 with several zeros and a trailing number.

Mitigation techniques include using Python's Decimal module or rounding techniques. Using the Decimal module with a custom level of precision.

Example:

from decimal import Decimal
Decimal('0.1') + Decimal('0.2') = 0.3

OR

from decimal import Decimal, getcontext
getcontext().prec = 1
Decimal(0.1) + Decimal(0.2) = 0.3

Typecasting

Used to modify the data type of one item to another, such as a string to an integer. Often used to modify user input to work with it for math.

Example:

  • If "123" is given as a string, using the int function changes it to the integer 123. Practical use includes calculating ages or prices from input strings using int() or float(), depending on the type of number needed.

Python's input() function accepts user input, while the print() function displays output in the terminal.

Customizing the print function with optional parameters

  • sep: Defines the separator between multiple arguments.
  • end: Determines what is printed at the end of the output.

Example:

print("Hello", "World", sep=", ", end="!")
# Expected output: Hello, World!

The default value of sep is an empty whitespace. The default value of end is a new line \n .

int() and float() functions

Use the int() function to convert input into integers. Use the float() function to convert input into floating-point numbers.

Example:

age = int(input('Enter your age: '))
height = float(input('Enter your height: '))
print(f'You are {age} years old and {height} meters tall.')