3.1.1 - What are variables

Sharon Kodali

Variables: an abstraction inside a program that can hold a value

A variable can be thought of as a container or a box that holds information that your program can use or modify

Variables help you manage and organize your work with data, making your code more organized, readable, and adaptable.

different data types to store variables in

  • integer used to store numbers that can later be used in mathematical operations ex: age or temperature
  • Text(string) Used to store texts lists and words that can later be referenced ex: Name, phone number, or address
  • Boolean used to store simply of true or false ex: is it raining

Correct way to name variables

incorrect: my highs-coreinthegame or n

  • too long and can make the code messy
  • dashes are not allowed when naming variables
  • spaces are not allowed when naming variables
  • descriptive enough to easily recall what the variable repersents

correct: highscore or numstudents or israining

  • short
  • descriptive
  • easy to distingush type of variable

3.1.1 Hacks

instructions: Determine what would be the the best variable name and data type for the specific prompt

  • storing if someones pet is a dog
  • storing someones birthday
  • storing the amount of money someone is spending
  • storing if it is sunny

Homework: write a greeting using variables in python

Naming Conventions

- Must start with a letter or an underscore
- Cannot start with a number 
- Can only have alphanumeric characters or underscores 
- Are case sensitive 
- Cannot be python keywords such as 'else'

myName = "Tara"
print(myName)

Tara

1Tara = "16"

  Cell In[2], line 1
    1Tara = "16"
    ^
SyntaxError: invalid decimal literal

myAge = 16 
myage = 46

print(myAge)
print(myage)

else = 22

Primitive v. Collection Data Types

Primitive Data Types

- int 
- string 
- float 
- boolean

Collection Data Types

- list 
- dictionary 

myInt = 20

myString = "My name is Tara"

myFloat = 77.29

myBool = False 

agesOfMyFriendsList = [16, 20, 15, 12]

print(agesOfMyFriendsList)

agesOfMyFriendsDictionary = { "Tara" : 16, "Tanisha" : 15, "Dylan" : 12, "Tara " : 17}


print(agesOfMyFriendsDictionary["Tara"])

print(agesOfMyFriendsDictionary["Tara "])

Concatenation

‘Joining’ of strings and other types

myFirstName = "Tara"

myLastName = "Sehdave"

print(myFirstName + " " + myLastName)

myFirstInt = 5

mySecondInt = 10 

print(myFirstInt + mySecondInt)

Formatting allows us to display values using pre-decided rules

message = "My first name is {0} and my last name is {1}"

print(message.format("Tara", "Sehdave"))

print(message.format("Tanisha", "Patil"))

x = .77 

message = "Show this as a percentage {0:.0%}"

print(message.format(x))

print(message.format(.25))

message = "The binary value of {0} is {0:b} and the binary value of {1} is {1:b}"

print(message.format(7, 6836))

Conversions

import json

myDictionary = {"A": 1, "B": 2}

print(myDictionary) 

myStringDictionary = json.dumps(myDictionary)

print(myStringDictionary)

myDictionaryRecreated = json.loads(myStringDictionary)

print(myDictionaryRecreated)


# Python Data Types in CB Pseudo Code 

## Primitive Types 

a <-- expression 
- myInt <-- 18
- myString <-- "My name is Tara"
- myFloat <-- 6.8
- myBool <-- False 

# Collection Types 

- myList <-- [1, 2, 3]
- No dictionary

Data Type Practice

Question 1: Integer Operation

  1. Declare two integer variables, num1Int and num2Int, and assign them values of your choice.
  2. Calculate the sum of num1Int and num2Int
  3. Print the sum

Question 2: Float Operation

  1. Declare two float variables, float1 and float2, and assign them values of your choice.
  2. Calculate the quotient of ‘float1’ and ‘float2’
  3. Print the quotient

Question 3: Format Manipulation

  1. Write a message that equals a sentence with two placeholder variables
  2. Write two strings with two placeholder variables to insert into the message
  3. Print that message

Answers

# Integer Operations

num1Int = 16

num2Int = 12

print(num1Int + num2Int)

# Float Operation

float1 = 1.00

float2 = .75 

print(float1 / float2 )

# Format Manipulation 

message = "{0} is {1} years old"

print(message.format("Tara", "16"))

print (message.format("Sharon", "8"))

print (message.format("Dylan", "80"))

☆ Topic 3.2 ☆

☆ Using lists as an abstraction to manage a program's complexity

☆ learn about the lists section of the exam reference sheet

Things to remember

  • use lists to store multiple elements
  • data abstraction provides a seperation between abstract parts of a datatype and the actual details of it
  • it can be created using lists
  • the exam reference sheets has list notations
  • the reference sheet has a list structure with index values 1-#of elements in the list. if list index is less that 1 or greater than the list
  • variables must be bundled together
    • strings, characters, words, numbers
  • give one name to a set of cells
num =[1, 2, 3, 4]
abc = ["a", "b", "c"]
colors = ["red", "green", "blue"]
emptylist = []

#replacing
alist = [10, 20, 30, 40, 50]
blist = [20, 40, 60, 80, 100]
alist = blist

print(alist)
#what will be the output of this code?


%%javascript
# Define an array with elements
const colors = ["Red", "Green", "Blue", "Yellow"];
# Access elements using indexes
const firstColor = colors[0]; // Index 0: "Red"
const secondColor = colors[1]; // Index 1: "Green"
#  Modify an element at a specific index
colors[2] = "Purple"; // Index 2 is changed from "Blue" to "Purple"
# Add a new element to the array
colors.push("Orange"); // Adds "Orange" to the end of the array
# Print elements and their indexes
console.log("First Color:", firstColor);
console.log("Second Color:", secondColor);
console.log("Updated Colors Array:", colors);
# Define a string
const greeting = "Hello, World!";
# Print the string
console.log(greeting);

3.2.3 Data Abstraction

-Manages complexity of data collection -Program easier to develop and maintain -Lists -If a list index is less than 1 or greater than the length of the list, an error message will be produced

How lists help with complexity

-Less variables (like one variable that holds multiple numbers instead of one variable for each number) -Changes number of variables -Consistency -Helps readability

Example

variable1 = 2 variable2 = 5 variable3 = 4

Would be simplified like this!

scores = [2, 5, 4]

Activity - Turn this into a list!

variable1 = 7 variable2 = 9 variable3 = 2 variable4 = 8