Python Key Skills

• Comparators check if a value is (or is not) equal to, greater than (or equal to), or less than (or equal to) another value.
• The result of comparator operation is always a Boolean vale - True or False
• Depending on the comparing outcome, the program then decide what to do next.
• Python has the following comparators:
  • logical operators
    • Equality, ==
    • Not equal, !=
    • Greater Than, >
    • Less Than, <
    • Greater than or equal to, >=
    • Less than or equal to, <=
  • Boolean operators: and, or, not
    • and: evaluates to True when both clauses (expressions) are True
    • or: evaluates to True when either of the expressions are True
    • not: evaluates to True when the expression is False. Evaluates to False when the expression is True.
• Example usages of comparators

hunger = True
numberOfPizza = 5
drink="fizzyPop"

if numberOfPizza >= 3:
   print("Have some pizza, since we have 3 or more")
else:
   print("You cannot have any pizza")


if hunger == True and numberOfPizza >= 1:
   print("You are hungry, and there is at least one pizza")
else:
   print("Either you are not hungry or the food is not pizza")

if not drink == "fizzyPop":
   print("No drink for me.")

#The above is same as:
if drink != "fizzyPop":
   print("No drink for me.")

• Each individual data pieces is called an item
• Each item has a position number called index
• For the following array, names, "Jack" is at index 0.
• To get "Jack", you use names[0]

# An array of strings
names = ['Jack', 'Kerry', 'Julia', 'Matthew', 'David']

• Swap the position of "Jack" with "Julia"
  1. Method 1: use a temporary variable

     names = ['Jack', 'Kerry', 'Julia', 'Matthew', 'David']
     
     temp = names[0]
     names[0] = names[2]
     names[2] = temp
     

  2. Method 2: in place swap

     names = ['Jack', 'Kerry', 'Julia', 'Matthew', 'David']
     
     names[0],names[2] = names[2],names[0]
     

• In Python, to generate random numbers, you use a module call random
• At the start of your program/code, you need to import the module random
  1. exmaple 1: generate a random whole number from 0 up to a limit

     import random
     
     randomNumber = random.randrange(100)
     # The above code picks a random number between 0 and 99
     
     randomNumber = random.randrange(2, 10, 2)
     # The above code picks a random number from 2, 4, 6, 8 (goes up by 2)
     

  2. exmaple 2: generate a random number between a range

     import random
     randomNumber = random.randint(1, 100)
     # The above code picks a random whole number between 1 and 100
     
     randomNumber = random.randint(50, 100)
     # The above code picks a random whole number between 50 and 100
     

  3. example 3: pick a random item from a list

     import random
     
     names = ['Jack', 'Kerry', 'Julia', 'Matthew', 'David']
     
     randomIndex = random.randrange(len(names))
     
     print("The random picked name is: ", names[randomIndex])
     

• In maths, we know that if a number A is a multiple of number B, it means A/B will not have a remainder - the remainder is 0.
• In Python, there is an operator for computing remainder conveniently. The operator is called modulo which is %
• Example 1

A=40
B=5
A%B will output 0

• Example 2

A = 12
B= 9
A%B will output 3 since 12 only contains one 9, the remainder is 12- 1 x 9=3

• Example 3

A = 9
B= 12
A%B will output 9 since 9 contains zero 12, the remainder is 9 - 0 x 12 = 9

• This remainder operator can be used to check if a number is even or odd

num = int(input("Give me a number: "))

if num % 2 == 0:
   print("It's an even number")
else:
   print("Not an even number")