Operators

• Operators are used to perform operations on values.

• The most basic are arithmetic operators, that are similar to regular arithmetic maths.

An example where basic arithmetic operators are used is:

a = 3
b = 2
c = a + b # c holds the value of 5

Modulo Operator

• A modulo operator (%) tells you what’s left after dividing one number by another.

  • dividend: The number being divided.

  • divisor: The number that divides the dividend.

  • result: The remainder of the division.

• Often used to check if a number is odd or even.

  • If a number is even, dividing it by 2 will leave a result of 0.

  • If a number is odd, dividing it by 2 will leave a result of 1.

result = dividend % divisor

result = 10 % 3

10 is divided by 3. 3 goes into 10 three times, with the remainder left that cannot be divided being 1. So the result will be 1.

Arithmetic Shortcuts

• Python has shortcuts for self arithmetic operations.

a = 5
a = a + 3 # a holds value 8

Can be simplified to:

a = 5
a += 3 # a holds value 8

The operator += adds the value 3 to a.

This can be applied to:

Comparison Operators

• Comparison operators are operators used to compare two operands.

• Used to check if operand is greater, less than or equal to other operand.

Logical operators

• Logical operators are used to combine conditional statements

• Python has three logical statements:

  • and, here’s an example:

    # Create two boolean variables
    x = True
    y = True
    
    # Check if both x and y are True
    result = x and y
    
    # Result will be True
    result = True

  • or

  • not

Example on how to use logical operators:

# Code determines elegibility to drive based on min. age of 18 and license status

age = 20 # Person is 20 
has_license = True # Person has license

result = age >= 18 and has_license
result = True # Eligible to drive

“Truth table”

• A truth table shows the combination of logical operators returns.

• Different table for each logical operator.

and

• The only way to get true, is if a and b or both true.

or

• To get true, a or b should be true.

not

• If a is false, then not a is true.

Multiple conditions

• Logical operators can have multiple conditions.

• To check if a number is positive and even, the following code can be written:

# Here are two conditions

is_postive = number > 0 # Number is above 0
is_even = number % 2 == 0 # Number can be divided by 2

# Conditions combined
result = is_postive and is_even 

# When result is true, both conditions are met.

# This can be done with less variables.
result = number > 0 and number / 2 == 0

Simplification and rearranging

• Logical expressions can be simplified and rearranged.

  • Ex. not in front of two conditions joined by and, can be split into two. Therefore and becomes or and each part gets its own not.

  • not (A and B) is the same as (not A) or (not B)

• Here simplification is used to see if a number upholds both variables as True:

# Check if a number is not between 1 and 10.
number = 15

# These expressions are equivalent, result 2 is simplified:
result1 = not (number >= 1 and number <= 10)
result2 = (not number >= 1) or (not number <=10)

print(result1)  # True
print(result2)  # True