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Python Key Skills

Python Key Skills

Learn It - convert from number data type to string

myName = "Jack"   # A string
myAge = 5         # A number

# To convert myAge to a string so we can make a longer string to display:
print(myName + " : " + str(myAge))

Learn It - comparing values and comparators

  • 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.")

Learn It - create an array of numbers or strings

# An array of numbers
testScores = [98, 78, 65, 89, 75]

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

Learn It - array index and get an item from an array

  • 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']

./img/arrayIndex.png

Learn It - swap the positions of two items in an array

  • 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]

Learn It - generate random numbers

  • 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])

Learn It - Find out of a number is a mulitple of other number

  • 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")