Hi, myself AuRa!
This is my project which has Scientific and Standard Calculator combined, made in python using Tkinter module based on GUI.
The Calculator is built in such a way that it first allows the user to enter the expression or the complete equation just like an actual scientific calulator in your device and then on pressing the equal-to button, it shows the result.
Though it may look like a long code, but it is very easy to understand. I tried to shorten it as much as possible. It works very efficiently and fastly for as many functions you enter in a single expression it will evaluate it correctly.
Here's a preview of how the GUI would look-