Calculadora Tkinter

import re
import tkinter as tk
from math import sqrt

class Application(tk.Frame):
    def __init__(self, master=None):
        super().__init__(master=master)
        self.master = master
        self.pack()

        self.input = '0'
        self.draw_frame()

    def create_button(self, text, color, command, r, c, cspan=1, w=8):
        self.button = tk.Button(self, bg=color, fg='white')
        self.button['text'] = text
        self.button['command'] = command
        self.button.config(height=2, width=w)
        self.button.grid(row=r, column=c, columnspan=cspan, pady=4)

        return self.button

    def draw_frame(self):
        self.label = tk.Label(self, font=("Helvetica", 16), bg='gray30', fg='white', anchor='se')
        self.label['text'] = '0'
        self.label.configure(width=23, height=5)
        self.label.grid(row=0, column=0, columnspan=4, pady=10)

        self.ce = self.create_button('CE', 'red2', self.clear, 1, 0)
        self.back = self.create_button(u'\u232b', 'gray20', self.back, 1, 1)
        self.mod = self.create_button('%', 'gray20', lambda : self.get('%'), 1, 2)
        self.div = self.create_button('/', 'gray20', lambda : self.get('/'), 1, 3)

        self.seven = self.create_button('7', 'gray20', lambda : self.get('7'), 2, 0)
        self.eight = self.create_button('8', 'gray20', lambda : self.get('8'), 2, 1)
        self.nine = self.create_button('9', 'gray20', lambda : self.get('9'), 2, 2)
        self.mul = self.create_button('X', 'gray20', lambda : self.get('*'), 2, 3)

        self.four = self.create_button('4', 'gray20', lambda : self.get('4'), 3, 0)
        self.five = self.create_button('5', 'gray20', lambda : self.get('5'), 3, 1)
        self.six = self.create_button('6', 'gray20', lambda : self.get('6'), 3, 2)
        self.minus = self.create_button('-', 'gray20', lambda : self.get('-'), 3, 3)

        self.one = self.create_button('1', 'gray20', lambda : self.get('1'), 4, 0)
        self.two = self.create_button('2', 'gray20', lambda : self.get('2'), 4, 1)
        self.three = self.create_button('3', 'gray20', lambda : self.get('3'), 4, 2)
        self.plus = self.create_button('+', 'gray20', lambda : self.get('+'), 4, 3)

        self.root = self.create_button('v', 'gray20', lambda : self.get('v'), 5, 0)
        self.zero = self.create_button('0', 'gray20', lambda : self.get('0'), 5, 1)
        self.dot = self.create_button('.', 'gray20', lambda : self.get('.'), 5, 2)
        self.equal = self.create_button('=', 'gray20', self.output, 5, 3)

    def get(self, value):
        self.input += str(value)
        self.ops = ['+','-','*','/','%', 'v']

        if self.input[-1] in self.ops and self.input[-2] in self.ops:
            self.input = str(self.input[:-2] + self.input[-1])
        if self.input[0] == '0':
            self.input = self.input[1:]
        if self.input[0] in self.ops:
            self.input = self.input[1:]
            self.input = '0' + self.input

        self.label['text'] = self.input

    def clear(self):
        self.input = '0'
        self.label['text'] = self.input

    def back(self):
        self.text = self.input
        if len(self.input) == 1:
            self.clear()
        else:
            self.input = self.text[:-1]
            self.label['text'] = self.input

    def output(self):
        root_ = re.compile(r'v\d+')
        all_roots = re.findall(root_, self.input)
        if all_roots:
            for num in all_roots:
                calc = sqrt(int(num.lstrip('v')))
                self.input = re.sub(num, '*'+str(round(calc,3)), self.input)

                if self.input[0] == '*' :
                    self.input = self.input[1:]

        self.out = str(round(eval(self.input), 5))
        self.label['text'] = self.out
        self.input = self.out

root = tk.Tk()
root.geometry('300x400+433+234')
root.wm_title('Calculadora')
root.resizable(False, False)

app = Application(master=root)
app.mainloop()