The traditional equal sign "=" is known as the assignment token in Python. It is used to assign values to variables. "a = b" means "b is assigned to a."

The double equal sign "==" refers to equality in an expression. So to represent "a equals b", we would write "a == b". 

= versus == in Python

A good why to represent variables and their respective assignments on paper is through the use of a reference diagram, also known as a state snapshot. It shows the respective states or assignments for each variable at a given point in time.  

Reference Diagrams in Python

A variable defined inside a function and it can only be used/called within this function. Calling this variable outside of the function it is defined in will lead to an error. This is an important idea in Python, as new users are frequently confused over the scope of defined variables.

Local Variable

Use the equal sign ("=") with the variable name on the left and the value on the right. 

Examples:
- car_model = "Ford Taurus"
- Total_Cost = 400
- n = 18

Note that the equal sign does not mean "equal to" in this case. It should be read as "(Variable) refers to (Value)." For example, "n refers to 18." 

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A variable is where data values can be stored. Another way to say this is that a value can be referred to by its respective variable. Variables do not need to be declared with any particular type, and can even change type after they have been set.

Variables in Python

A value is any thing in the form of a number, string, character, etc. that can be manipulated. Values can also be referred to as objects. 

Values in Python

https://runestone.academy/runestone/books/published/fopp/index.html

Runestone: Foundations of Python Programming

http://pages.cs.wisc.edu/~calvin/cs110/LOCAL_GLOBAL.html#:~:text=A%20local%20variable%20is%20a,use%20them%20within%20that%20function.

Local Variable Reference Source

https://www.geeksforgeeks.org/global-local-variables-python/

Global Variable Reference

Variables, which store values, can have names of any length, but variables named with the following will be considered invalid:
- Have spaces 
- Start with numbers
- Possess illegal characters (i.e. $)
- Is a Python Keyword

As long as the variable name does not possess any of the above characteristics, it will be valid. 


Rules for Naming Variables 

Setting Variables in Python 

After setting variables, their assigned values can be updated through the use of operators. If the print() function is applied to the reset variable, the newly updated value will appear. 

Updating Variables in Python 

Hard Coding is the practice of writing code that can only satisfy one solution. While the hard-coded variable may be correct in a given circumstance, the overall logic of the code is not validated. 

The logic, flow, and computations should be depended on when writing code.

Why Not to Hard Code When Learning Python

Values can be classified into different classes, known as data types:
- Integer (int) - 1, 4, 7, 24, 578, etc.
- Float (float) - 2.2, 2.59, 3.14159, etc.
- String (str) - *Any combination of characters in quotes
- List (list) - An ordered, mutable collection of items
- Tuple (tuple) - An ordered, immutable collection of items
- Dictionary (dict) - An unordered collection of data with keys and values
- Boolean (bool) - True or False
 
The terms "data type" and "class" are often used interchangeably.

Data Types in Python

- Expressions are any combination of data types to be evaluated. Evaluating an expression results in values/objects. Expressions can also be evaluated into or set to values. 
- Asking Python to print an expression will result in the interpreter attempting to evaluate the expression and display the result

Expressions in Python 

Scope determines where a variable can be accessed. The two common Scopes are Local scope and Global scope.

Variables in Local scope are called local variables and these variables are defined inside a function. Local variables can only be accessed inside that function. Similarly, variables defined inside a loop of a function can only be accessed inside that loop. To use those variables outside of the loop in the rest of the function, they must be defined before the loop starts. 

Variables in Global scope are called global variables and these are defined outside functions. Global variables are accessible anywhere in the Python module.

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