Python: Data Types and Variables

Learning Objectives

• Using the correct data types, such as string, integer, or float, is important
• Key functions include int, float, and round
• Assignment statements must be used correctly
• Utilize the BIDMAS rule for arithmetic operations
• Develop a program that involves input, calculation, and output

Python Program Example

• The sample code takes user input for an animal's name and a description of the animal
• It then outputs a statement including the animal's name and description
• The program also extracts the first letter of the animal's name and includes it in another output statement

Data Types

• Strings hold alphanumeric characters like A-Z, a-z, 0-9 and symbols, treated as text
• Integers represent whole numbers
• Floats represent numbers with decimal points
• Booleans represent True or False

Defining Variable Data Types

• Python automatically assigns a data type to a variable
• It is possible to manually define a data type using:
  • str() to convert a value to a string, e.g., str(animal_name)
  • int() to convert a value to an integer, e.g., int(goals_scored)
  • float() to convert a value to a floating-point number, e.g., float(share_price)
• Manually defining or changing the data type of a variable is called Casting

Choosing Data Types

• Age (e.g., 14) would be stored as an Integer, and the code is int(age)
• Shoe Size (e.g. 6.5) is stored as a Float

Significance of Data Types

• When creating a variable (e.g., mynumber) and assigning a value to it using user input.
• The data type can be converted using mynumber = int(mynumber)

Assignment Statements

• Assignment statements assign a value to a variable
• If the variable doesn't already exist, it's created
• Examples:
  • name = "Jo" + "Smith"
  • number = 10
  • number = input("Enter a number")

BIDMAS

• The order of arithmetic operations is important and follows the BIDMAS rule
• BIDMAS stands for:
  • Brackets
  • Indices
  • Division
  • Multiplication
  • Addition
  • Subtraction

Arithmetic Operators

• Addition: +, e.g., 2 + 10 = 12
• Subtraction: -, e.g., 9 - 6 = 3
• Multiplication: *, e.g., 5 * 4 = 20
• Division: /, e.g., 5 / 2 = 2.5
• Floor Division: //, e.g., 7 // 2 = 3
• Remainder: %, e.g., 7 % 3 = 1

Sleep Calculator Program

• Can calculate the number of hours per week one sleeps
• The prompt presented is intended to find any errors in the code
• To find the total hours of sleep in a month:
  • Use the average of 4.35 weeks per month
  • hourspernight = input("How many hours per night do you sleep? ")
  • hoursperweek = int(hourspernight) * 7
  • print ("You sleep",hoursperweek,"hours per week")
  • hourspermonth = float(hoursperweek) * 4.35
  • print ("You sleep",hourspermonth,"hours per month")

Rounding

• Assign hours per month a value of 228.37499999999997
• round(hourspermonth) results in 228
• round(hourspermonth,2) results in 228.37
• Example code showing the rounding of value and printing value with rounding applied:
  • hourspernight = input("How many hours per night do you sleep? ")
  • hoursperweek = int(hourspernight) * 7
  • print ("You sleep",hoursperweek,"hours per week")
  • hourspermonth = float(hoursperweek) * 4.35
  • hourspermonth = round(hourspermonth)
  • print ("\nYou sleep",hourspermonth,"hours per month")

Program Finishing Touches

• Display a title when the program first runs
• Calculate the number of days per year spent asleep
• Include the user's name to personalize the program

Mobile Phone Cost Calculator App

• Consider following criteria when developing a mobile phone cost calculator app:
  • Accept the user’s name and mobile phone network
  • Ask for the number of minutes they have used this month
  • Multiply the minutes used by $0.10/minute
  • Ask for the number of texts that they have sent this month
  • Multiply the texts sent by $0.05 per text
  • Display a total bill amount for the month
  • Display a new total including VAT of 20%