3.1 Python Variables

Naming Conventions

There are many naming conventions for variables in programming.

snake_case

In snake case, words in variables are all lowercase and are separated by a comma. These are some examples:

foo_bar
one_two
peppa_pig

camelCase

In camel case, the first word is lowercase, and the first letter of the remaining words are uppercase. These are some examples:

fooBar
oneTwo
peppaPig

PascalCase

In pascal case, The first letter of each word is uppercase. These are some examples:

FooBar
OneTwo
PeppaPig

In Python, we use snake case for data.

Introduction to Variables in Python

A variables is used to store data in Python.

# Booleans

is_student = True
is_teacher = False
print(is_student)  # Output: True
print(is_teacher)  # Output: False

True
False

# Strings
# Strings are sequences of characters, used to store text.

greeting = "Hello, World!"
name = 'Alice'
print(greeting)  # Output: Hello, World!
print(name)  # Output: Alice

Hello, World!
Alice

# Dictionaries
# Dictionaries are collections of key-value pairs.
# Key-value pairs allow us to store and retrieve data using keys, which are identifiers.

student = {
    'name': 'Alice',
    'age': 25,
    'courses': ['Math', 'Science']
}
print(student['name'])  # Output: Alice
print(student['courses'])  # Output: ['Math', 'Science']

Alice
['Math', 'Science']

# Arrays (Lists)
# Lists are ordered collections of items.

numbers = [1, 2, 3, 4, 5]
fruits = ['apple', 'banana', 'cherry']
print(numbers)  # Output: [1, 2, 3, 4, 5]
print(fruits)  # Output: ['apple', 'banana', 'cherry']
greeting = "Hello, World!"
name = 'Alice'
print(greeting)  # Output: Hello, World!
print(name)  # Output: Alice

[1, 2, 3, 4, 5]
['apple', 'banana', 'cherry']
Hello, World!
Alice

# Dictionaries

student = {
    'name': 'Alice', # string
    'age': 25, # int
    'courses': ['Math', 'Science'] # list
}
print(student['name'])  # Output: Alice
print(student['courses'])  # Output: ['Math', 'Science']

Alice
['Math', 'Science']

# Arrays (Lists)

numbers = [1, 2, 3, 4, 5]
fruits = ['apple', 'banana', 'cherry']
print(numbers)  # Output: [1, 2, 3, 4, 5]
print(fruits)  # Output: ['apple', 'banana', 'cherry']

[1, 2, 3, 4, 5]
['apple', 'banana', 'cherry']

1. Which of these commands will write "Hello"?

print("Hello")
Print(Hello)
print"Hello"

2. Which of these do you use to create an empty dictionary?

()
[]
{}

3. Given arr = ['apple', 'banana', 'cherry'], which of these equates to "cherry"?

arr[0]
arr[1]
arr[2]