2. Python: Data Types & Containers

• Comments: A hash sign # in a code block begins a comment. All characters after the # and up to the end of the physical line are part of the comment and the Python interpreter ignores them. It’s like a note or reminder that programmers leave for themselves or others who read their code. It's written in plain English and doesn't affect how the program runs. Comments help explain what the code does, making it easier to understand and work with, so we’d highly recommend getting into the habit of writing comments!

# This is how you write a comment

✏️
Try-It | Text & Code Cells
Continue working in the same Colab notebook to complete the following tasks:
1. Create a text cell with notes about things you want to remember from this lesson. Include text that is bold, italicized, different font sizes, or organized in lists!
2. Create a code cell and print() an encouraging message to yourself. Run the code cell to see the output below the code!

# String Example

"Karlie Kloss"

'Data Feminism'

print()

# Print out the following text
print('Hi, Kode With Klossy')

✉️ Variables

# Variable example
dog = "fluffy"

print(dog)

# Variable example 2
favorite_food = "pizza"

print(favorite_food)

String Methods

• lower()

• strip()

• replace()

text1 = "HeLLo, WoRLd!"
print(text1.lower())

text2 = "   Python is fun!   "
print(text2.strip())

text3 = "Coding is soooo cool!"
print(text3.replace("soooo", "so"))

text4 = "   WELCOME to Python!!!   "
cleaned_text = text4.strip().lower().replace("!!!", "")
print(cleaned_text)

messy_text = "   HeLlO, wOrLd!   "

• Integers are used to represent whole numbers (ex. 50)

• Floats are used to represent fractional or irrational numbers (ex. 3.14)

# Integer Example 
print(10)

# Float Example 
print(5.5)

# This is a string (not a number) because it has quotation marks. Python will treat this like a word, not a number.
print("15")

# convert float to integer 
int(1.999)

# convert integer to float 
float(4)

# convert float to string
str(1.999)

➗ Python as a Calculator

# Addition, subtraction
print(5 + 5)
print(5 - 5)

# Multiplication, division, and exponentiation
print(3 * 5)
print(10 / 2)
print(4 ** 2)

lucky_number = 2 * (45 - 2**2) - (12 / 2) + 1

#Do not remove brackets from the print function
print(lucky_number)

• Yes or No

• Correct or Incorrect

• Left or Right

• On or Off

is_member = True
print(is_member)

print(20 > 10)
print(100 == 50)
print(10 < 5)

is_member = True
pt_sessions = 4
is_eligible = is_member and pt_sessions < 4
print(is_eligible)

empty_list = []
print(empty_list)

# You can also use the list function to create a list.
empty_list = list()
print(empty_list)

# List containing only string types
food = ['pizza', 'sushi']

# List containing only numbers
numbers = [20,10,5]

# List containing multiple types
multitype = ['pasta', 100, 1.25]

Accessing Items in a List

# Creating a list of colors 
colors = ['blue', 'pink']

# printing item in list based on index 
print(colors[0])
print(colors[1])

Slicing

# create a list
letters = ['a', 'b', 'c', 'd', 'e','f']

# slice out the first 2 elements (elements at index 0 and 1)
print(letters[0:2]) # -> ['a', 'b']

# slice out the middle 2 elements 
print(letters[2:4]) # -> ['c', 'd']

# take the last 2 elements (starting at index 4 to the end of the list)
print(letters[4:]) # -> ['e', 'f']

# can also use the negative indices for slicing
print(letters[-2:]) # -> ['e', 'f']

# print every other element
print(letters[::2]) # -> ['a', 'c', 'e']

Slicing and Indexing on Strings

my_string = "Karlie Kloss"

# Pull out the first character of the string
print(my_string[0])

# Pull out the last character of the string
print(my_string[-1])

# Creating a substring of only some characters 
print(my_string[6:10])

# Creating a substring of only some characters 
print(my_string[-12:-7])

List Operations

# Add an item 
my_list = []
my_list.append('Value')
print(my_list)

# Remove an item
my_list.pop(0)
print(my_list)

• The name of the list we intend to update

• a . to show that we are using a method to update the list

• The name of the method we want to use and the appropriate parameters:
• If using the append method, include what we are adding to the list in quotation marks.
• If using the pop method, include the index of the item we are removing.

empty_dictionary = {}

my_dictionary = {'key1': 1, 'key2': [1,2,3]}

# Empty dictionary
myempty_dictionary = {}

# Equivalently
myempty_dictionary = dict()
print(dict())

Accessing Dictionary Values

# Access Data in a Dictionary
scholar_hometowns = {"Karlie": "Chicago", "Serena": "Los Angeles"}

print(scholar_hometowns["Karlie"])

type(scholar_hometowns)

scholar_hometowns["Serena"] = "Saginaw"
print(scholar_hometowns)

scholar_hometowns["Zendaya"] = "Oakland"
print(scholar_hometowns)

1. Lists of lists – a list where each element is also a list

2. Dictionaries with nested structures – a dictionary where some values are also dictionaries (or lists)

Lists of Lists

playlists = [
	["Enchanted", "Cool", "Feather"],
	["Shake It Off", "Physical", "Espresso"], 
	["Love Story", "New Rules", "Thumbs"]
]

Dictionaries with Nested Structures

user_profile = {
    "username": "MusicLover23",
    "email": "musiclover23@example.com",
    "subscription": "Premium",
    "playlists": {
        "Chill Vibes": ["Enchanted", "Cool", "Feather"],
        "Hype Mode": ["Shake It Off", "Physical", "Espresso"], 
        "Throwbacks": ["Love Story", "New Rules", "Thumbs"]
    },
    "top_artists": ["Taylor Swift", "Dua Lipa", "Sabrina Carpenter"],
    "listening_stats": {
        "minutes_listened": 34567,
        "most_played_song": "Espresso",
        "favorite_genre": "Pop"
    }
}

Immutable Types

my_str = 'abc'

#let's say I want to change my_str to be 'adc'
my_str[1] = 'd'

# I can only do that by redefining what my_str is
my_str = 'abc'
my_str = 'adc'
print(my_str)

Mutable Types

my_list = [1, 2, 3, 4, 5]
print(my_list)

# we can change what is stored in my_list
my_list[1] = 'new item'
print(my_list)

# we can also change the list by using a method 
my_list.append(3.14)
print(my_list)

Tuples

my_tuple = (1,2,3,4,5,'a string',4.99)
type(my_tuple)

my_tuple[1] = 9
my_tuple.append('new item')