I've recently finished building a calculator in python using tkinter, and would appreciate any and all feedback on it. Please ignore the use of the "eval" function, I know this is advised against using but my teacher insists that we use it in our development.

I'd really like to condense and simplify my code for validation which can be found below, but I can't think of any other way to do it. This code validates text being entered into the tkinter entry field.

I've recently finished building a calculator in Python using Tkinter, and would appreciate any and all feedback on it. Please ignore the use of the eval function, I know this is advised against using but my teacher insists that we use it in our development.

I'd really like to condense and simplify my code for validation which can be found below, but I can't think of any other way to do it. This code validates text being entered into the Tkinter entry field.

I'd really like to condense and simplify my code for validation which can be found below, but I can't think of any other way to do it. This code validates text being entered into the tkinter entry field.

def validate_input(self, entered_value, modify_type, index):#used to validate input entered into entry field.

    current_input = str(self.text_box.get())
    index_pos = int(index)
    
    #Cheecks if the attempted modification type is insertion or deletion.
    if modify_type == '1': #insert
            
        if entered_value== ".":
            if current_input == "":
                return True#allows a decimal point to be inserted if the field is blank.
            elif index_pos == len(current_input):
                if current_input[-1] == ".":
                    return False#doesn't allow a decimal to be inserted if the last character is a decimal.
                else:
                    return True
            elif current_input[index_pos-1] == "." or current_input[index_pos] =="." :
                return False#doesn't allow a decimal to be inserted if there is a decimal point on either side of the insert position.
            else:
                return True

        if entered_value in "*/+-":
            
            if current_input == "" and entered_value in "*/":
                return False#doesn't allow a multiplication or division operator to be entered into an empty field.
            elif current_input == "" and entered_value in "+-":
                return True#allows an addition or subtraction operator to be entered for negative and positive numbers
            
            if index_pos == len(current_input):#if character is being inserted at the end of the string
                if current_input[-1] in "+-" and entered_value in "+-":
                    return True#allows two addition or subtraction signs in a row.
                elif current_input[-1] == "." and entered_value in "+-":
                    return False#doesn't allow the insertion of + or - after a decimal point.
                elif current_input[-1] in "*/+-." and entered_value in "*/":
                    return False#doesn't allow * or / to be entered after */+-
                else:
                    return True
                
            if entered_value in "+-":
                if current_input[index_pos-1] in "*/+-" or current_input[index_pos] in "*/+-" :
                    return True#allows a + or a - to be inserted after or before another operator.
                elif current_input[index_pos-1] == ".":
                    return False#doesn't allow a + or a - to be entered after a decimal point.
            elif entered_value in "*/":
                if current_input[index_pos-1] in "*/+-." or current_input[index_pos] in "*/+-" :
                    return False#doesn't allow a * or / to be entered if there is an operator or decimal before, or an operator after.
            else:
                return True
            
        #Checks if entered value is in list of accepted values, stored in setup of CalculatorGUI class.
        if entered_value in self.accepted_values:
            return True

    #Accepts all attempts to remove text from the entryfield.
    elif modify_type == "0":#delete
        return True
    return False

Full code can be found below, thanks for your help! :)

from tkinter import *
from tkinter import messagebox
import re

class CalculatorFunctions:
    def __init__(self, root):
        self.root = root

    def num_press(self, num):#function that runs if a number button is pressed
        new_input = num
        cursor_position = self.text_box.index(INSERT)#gets position of where number is trying to be inserted
        self.text_box.insert(cursor_position, new_input)#inserts number at the cursor's position in the entry field

    #Creates a message-box popup to display relevant author information.
    def show_info_popup(self):
        messagebox.showinfo("Author", "NAME", \nLast Edited: September 2018\nPython Version: 3.7.0")

    #Command that clears everything in the calculator's entrybox.
    def clear_screen(self):
        self.text_box.delete(0, END)

    #Removes the last character in the entry field.
    def backspace(self):
        current = str(self.text_box.get())
        cursor_position = self.text_box.index(INSERT)
        if cursor_position == 0:#if the insert position is at the beginning of the entry field (far left), don't backspace anything.
            pass
        else:
            #deletes the text one index position before the insert position.
            cursor_position -= 1
            self.text_box.delete(cursor_position)

    #Uses the eval function to calculate entered string in calculator.
    def calculate_answer(self):
        try:
            #regex string that removes leading zeroes from the start of numbers and replaces the matched pattern with the numbers found in group 2.
            answer = eval(re.sub(r"((?<=^)|(?<=[^\.\d]))0+(\d+)", r"\2", self.text_box.get()))
            self.accepted_values.append(str(answer)) #appends answer to list of accepted values so that it is able to be inserted into the entry field through the validation algorithm.
            self.text_box.delete(0, END) #deletes contents of entry field.
            self.text_box.insert(0, answer)#inserts answer into entry field.
        except (SyntaxError, ZeroDivisionError):#runs if a syntax error or zero division error is caught when calculating an answer.
            messagebox.showwarning("Error", "Please edit your entered input and calculate again.\nCommon errors include:\n\n -Dividing by 0\n -Including too many decimal points in one number\n -Incorrect operator usage\n- Pressing equals when the screen is empty")

    def validate_input(self, entered_value, modify_type, index):#used to validate input entered into entry field.

        current_input = str(self.text_box.get())
        index_pos = int(index)
        
        #Cheecks if the attempted modification type is insertion or deletion.
        if modify_type == '1': #insert
                
            if entered_value== ".":
                if current_input == "":
                    return True#allows a decimal point to be inserted if the field is blank.
                elif index_pos == len(current_input):
                    if current_input[-1] == ".":
                        return False#doesn't allow a decimal to be inserted if the last character is a decimal.
                    else:
                        return True
                elif current_input[index_pos-1] == "." or current_input[index_pos] =="." :
                    return False#doesn't allow a decimal to be inserted if there is a decimal point on either side of the insert position.
                else:
                    return True

            if entered_value in "*/+-":
                
                if current_input == "" and entered_value in "*/":
                    return False#doesn't allow a multiplication or division operator to be entered into an empty field.
                elif current_input == "" and entered_value in "+-":
                    return True#allows an addition or subtraction operator to be entered for negative and positive numbers
                
                if index_pos == len(current_input):#if character is being inserted at the end of the string
                    if current_input[-1] in "+-" and entered_value in "+-":
                        return True#allows two addition or subtraction signs in a row.
                    elif current_input[-1] == "." and entered_value in "+-":
                        return False#doesn't allow the insertion of + or - after a decimal point.
                    elif current_input[-1] in "*/+-." and entered_value in "*/":
                        return False#doesn't allow * or / to be entered after */+-
                    else:
                        return True
                    
                if entered_value in "+-":
                    if current_input[index_pos-1] in "*/+-" or current_input[index_pos] in "*/+-" :
                        return True#allows a + or a - to be inserted after or before another operator.
                    elif current_input[index_pos-1] == ".":
                        return False#doesn't allow a + or a - to be entered after a decimal point.
                elif entered_value in "*/":
                    if current_input[index_pos-1] in "*/+-." or current_input[index_pos] in "*/+-" :
                        return False#doesn't allow a * or / to be entered if there is an operator or decimal before, or an operator after.
                else:
                    return True
                
            #Checks if entered value is in list of accepted values, stored in setup of CalculatorGUI class.
            if entered_value in self.accepted_values:
                return True

        #Accepts all attempts to remove text from the entryfield.
        elif modify_type == "0":#delete
            return True
        return False

class CalculatorGUI(CalculatorFunctions):
    
    def __init__(self, root):
        self.root = root
        #binds equals key to calculate an answer when pressed
        root.bind("=", lambda event: self.calculate_answer())
        #binds enter key to calculate an answer when pressed
        root.bind('<Return>', lambda event: self.calculate_answer())
        #list of values allowed to be inserted into entry field
        self.accepted_values = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "+", "-", "*", "/", "."]
        self.create_number_buttons()
        self.create_text_box()
        self.create_special_buttons()

    def create_number_buttons(self):
        button_characters = "789*456/123-0.=+"
        #Variable that is used to iterate through button characters.
        i = 0
        #Empty list to store created buttons in.
        self.button_list = []
        #Row starts at row 2 as I will have the entry field on row 0 and AC on row 1.
        for row_counter in range(2,6):
            #I want to have a 4x4 grid of buttons, so will use column in range 4 (0,1,2,3) for each row.
            for column_counter in range(4):
                #Appends each button to a list as it is created so that individual buttons are able to be referenced at later stages of program development.
                self.button_list.append(Button(root, bg="#11708e", fg="white", pady=25, padx=35, text=button_characters[i], font=("Helvetica", 20, 'bold')))
                self.button_list[i].grid(row=row_counter, column=column_counter, sticky="NSEW")
                self.button_list[i].configure(command = lambda character=button_characters[i]: self.num_press(character))
                i += 1

                self.reconfigure_operator_buttons()

    #Reconfigures operators ro have a red background.
    def reconfigure_operator_buttons(self):
        i = 0
        for button in self.button_list:
            #Cget gets the current value of the specified button attribute, in this case being "text".
            if self.button_list[i].cget("text") in "-+/*.=":
                self.button_list[i].configure(bg="#d14302")
                
                if self.button_list[i].cget("text") == "=":
                    self.button_list[i].configure(command=self.calculate_answer)
            i +=1

    def create_text_box(self):
        self.text_box = Entry(root, justify=RIGHT, validate="key", font=("Helvetica", 20, 'bold'), borderwidth=15)
        self.text_box['validatecommand'] = (self.text_box.register(self.validate_input),'%S','%d', '%i')
        #Places the entry field in row 0, column 0, adds internal padding to increase width of field.
        self.text_box.grid(row=0, column=0, columnspan=4, ipady=10, sticky="WE")

    def create_special_buttons(self):
        
        clear_button = Button(root, bg="#302e2e", fg="white", text="AC", font=("Helvetica", 14, 'bold'), pady=10,command=self.clear_screen)
        clear_button.grid(row=1, columnspan=2, sticky="WE")

        backspace_button = Button(root, bg="#302e2e", fg="white", text="Backspace", font=("Helvetica", 14, 'bold'), pady=10, command=self.backspace)
        backspace_button.grid(row=1, column=3, sticky="NSEW")

        author_button = Button(root, bg="#302e2e", fg="white", font=("Helvetica", 14, 'bold'), text="Info", pady=10, command=self.show_info_popup)
        author_button.grid(row=1, column=2, sticky="NSEW")


root = Tk()
root.title("Calculator")
root.resizable(0, 0)
calc = CalculatorGUI(root)
root.mainloop()