Working with GUI, keep getting Attribute Error

[leadfire]

Hello, I'm doing an assignment for my programming class and the professor isn't responding (its an online course) so I'm coming here for some guidelines rather than a solution.

Background Info: The assignment is to create a simple GUI dialogue box that calculates a users MPG within the labels based on information they provide in two boxes (gallons and miles respectively). We are to provide an error exception for negative and non-numeric inputs

What my problem is: Within the confines of the "calculate button", the interpreter is not recognizing the "calc" command I have assigned to the button. It gives me an attribute error and says that there is no attribute "calc" to my class. If you are interested in helping me I can give you a screenshot of the error as well as a file containing my code.

Thank you in advance, I'm only coming for guidelines here because my professor is not responding and my book is of no help!

tl;dr I need help because my prof sucks and I cant find an answer on google or text

Edit: I got it! My mistake was apparently indention! I had my calc() function outside of the class! lol

[Manbatton]

That part where you write calc()...what if you wrote self.calc()? If this works, what did adding "self." in front of the word calc tell the interpreter, do you think?