Create a GUI Calculator using the tkinter library in Python

This project was created to test logical knowledgements and practice. If you can help me understanding how can i write better the code, please be free to show me how i can do it.

Thanks!

Basically, the code works with the value of the label master, which is updated as the buttons are used (numbers, operations, etc.)

When i press "1" for example, this value is set to 1; so when i press "+", this value will be storaged in a variable that is known as bfnumber (before number), a global variable will storage the value that represents the operation "+" (like "1"), and the value of the label is returned to "0", waiting for a new call to change this number. When this other number is typed, the program have two numbers and a operation to calculate clicking or not in "=".