The most advanced calculator with a bunch of functions supported.
including sin, cos, tan, log any base, summation, definite integration and definite differentiation
This is a stand-alone file that you can use.
However, if you want OOP that resembles the true structure of a tree,
you would want ParserWithTree.py, CalculationTree.py and additionally Visualizer.py
That is the file that contains the OOP stuff.
Node is defined there.
Its the same as Parser.py, but instead of calculating in-place, it creates Nodes.
The Node class has evaluate() method that calculates it's value.
Used to visualize the expression tree. (Turtle)
There is the same thing but in JavaScript.