Messagebox

[carecavoador]

You don't need to assign messagebox to a variable. Just call messagebox.showerror straight away.

As @menator01 said, it's bad practice to import everything from a module. In this case, you don't even need to import anything else than messagebox.

Also, don't forget to break from the while loop or you will be stuck in it forever.

from tkinter import messagebox

def math():
    while True:
        data = input("enter a,b or c ")
        if data == 'a':
            data=5
        elif data == 'b':
            data=10
        elif data == 'c':
            data=15
        else:
            messagebox.showerror(title="Try",message="Wrong Input")
            data=0
        print(data)
        break

if __name__ == "__main__":
    math()