Variables

Containers for storing data
The value can change when a variable is mutable
Because Python is dynamically typed, variables must be declared and assigned in the same statement
- You can use None if you don’t want a value yet.
In Python, you need a name and a value for a variable.
- You can optionally add a type, such as str

cheese: str = "mozarella"
#       ^ optional type

Assignment

Assignment operator (=)
- The value on the right is assigned to the variable on the left.
- IE: cheese = "mozarella"
Variables can be re-assigned to any type.
- If you have a type hint for the variable, your IDE should stop you, but Python itself doesn’t care.

Numeric data and non-numeric data
- int → integers
- float → decimal numbers
- str → a list of characters; text data
- bool → True or False

age = 69 # int
gpa = 0.1 # float
name = "skibidi toilet" # str
is_cool = True # bool

x = 3.0
 
print(type(x)) # <class 'float'>
print(type(x) === float) # True

Changes the data type of a variable to another
Normally you’d have to use a casting operator, such as as
In Python, you have to use the casting functions, such as int(), float(), and str()
- These functions can raise errors when converting invalid values
- float → int will truncate

x = "some string"
x = int(x) # ValueError: invalid ltieral for int()
 
y = 2.99
y = int(y) # ⌊2.99⌋ = 2

In Python, division between two integers always results in a float, unless you use integer/floor division //:

x = 15
y = 7
 
x / y # 2.14... (float)
x // y # 2 (int)

4 % 2 # 0
4 % 3 # 1

Represented by the str class in Python
Concatenation → combining two or more strings
- You can only concatenate strings with other strings (or you raise a TypeError)
- IE: "me" + "ow" → "meow"
Interpolation → inserting different things into a string
- You can use the .format method on strings, or an f-string
- IE: f"i am {x} years old (where x is an int)

You can get the character from a certain index using the str[idx] syntax.
- IE: "Hello"[0] → "H", "Hello"[-1] → "o"
You can get the length of a string using the len() function
- IE: len("ABC") → 3
You can slice strings using the str[start:stop:step] syntax.
- The stop option is exclusive, and you can skip options
- IE: "Hello"[0:4] → "Hell", "Hello"[0::4] → "Ho"

You can reverse a string with slicing by using [::-1]

Comments should describe the why not the what