A basic python REPL application to calculate simple mathematical equation

The App is divided into:

1. The main interface
2. The Validator, to validate the inputs
3. The Tokenizer, to transform validated inputs into list of tokens
4. The Calculator, to calculate tokenize equation into digit
5. The Command, to call the built in commands from inputs
6. The Exception, to represent custom errors
7. The Variable to represent a variable
8. The Digit to represent the numeric operands
9. The Operator to represent the Operator
10. The Memory to represent as a store for numeric value of Variable

1. Store and use variables in your equation!
2. Parenthesis, Multiplication, Division, Exponentiation, Addition, Subtraction and Assignment!
3. Stuck? use help! (/help)

python calculator/calculator.py

> 8 * 3 + 12 * (4 - 2)
48
> 2 - 2 + 3
3
> 4 * (2 + 3
Invalid expression
> -10
-10
> a=4
> b=5
> c=6
> a*2+b*3+c*(2+3)
53
> 1 +++ 2 * 3 -- 4
11
> 3 *** 5
Invalid expression
> 4+3)
Invalid expression
> /command
Unknown command
> /exit
Bye!

Tested to work and run properly on python 3.8.5