Problem using a button with tkinter

[SmukasPlays]

I'm new on Python and now I'm trying to do a simple product registration system with tkinter and sqlite3, following a tutorial on the internet. But I'm having some problems and I don't know what to do.

My code:

from tkinter import *
import sqlite3
import tkinter.messagebox


conn = sqlite3.connect("C:\TkinterVenda\Database\store.db")
c = conn.cursor()

result = c.execute("SELECT MAX(id) from inventory")
for r in result:
    ID = r[0]

class Database:

    def __init__(self, master, *args, **kwargs):

        self.master = master
        self.heading = Label(master, text="Cadastro De Produtos", font = ('arial 40 bold'), fg = 'steelblue')
        self.heading.place(x=400,y=0)

        self.Name_1 = Label(master, text = "Nome do produto:", font= ('arial 18 bold'))
        self.Name_1.place(x=0, y=70)

        self.Stock_1 = Label (master, text="Estoque:", font=('arial 18 bold'))
        self.Stock_1.place (x=0, y=120)

        self.CP_1 = Label (master, text="Preço Custo:", font=('arial 18 bold'))
        self.CP_1.place (x=0, y=170)

        self.SP_1 = Label (master, text="Preço Venda:", font=('arial 18 bold'))
        self.SP_1.place (x=0, y=220)

        self.Vendor_1 = Label (master, text="Nome do Fornecedor:", font=('arial 18 bold'))
        self.Vendor_1.place (x=0, y=270)

        self.Vendor_PhoneNumber_1 = Label (master, text="Telefone do Fornecedor", font=('arial 18 bold'))
        self.Vendor_PhoneNumber_1.place (x=0, y=320)

        self.ID_1 = Label (master, text="ID:", font=('arial 18 bold'))
        self.ID_1.place (x=0, y=370)

        self.Name_e = Entry(master, width = 25, font=('arial 18 bold'))
        self.Name_e.place (x=300, y=70)

        self.Stock_e = Entry (master, width=25, font=('arial 18 bold'))
        self.Stock_e.place (x=300, y=120)

        self.CP_e = Entry (master, width=25, font=('arial 18 bold'))
        self.CP_e.place (x=300, y=170)

        self.SP_e = Entry (master, width=25, font=('arial 18 bold'))
        self.SP_e.place (x=300, y=220)

        self.Vendor_e = Entry (master, width=25, font=('arial 18 bold'))
        self.Vendor_e.place (x=300, y=270)

        self.Vendor_PhoneNumber_e = Entry (master, width=25, font=('arial 18 bold'))
        self.Vendor_PhoneNumber_e.place (x=300, y=320)

        self.ID_e = Entry (master, width=25, font=('arial 18 bold'))
        self.ID_e.place (x=300, y=370)

        self.btn_add =  Button(master, text = "Cadastrar", width=25, height = 2, bg='steelblue',fg = 'black', command = self.get_items)
        self.btn_add.place (x=520, y=420)

        self.btn_clear = Button (master, text="Limpar", width=18, height=2, bg='red', fg='black', command = self.clear_all)
        self.btn_clear.place (x=350, y=420)

        self.textBox = Text (master, width=60, height = 18)
        self.textBox.place (x=750, y=70)
        self.textBox.insert(END, "Ultimo ID Cadastrado: " + str(ID))

        self.master.bind('<Return>',self.get_items)
        self.master.bind('<Up>', self.clear_all)

    def get_items(self, *args, **kwargs):

        self.Name = self.Name_e.get()
        self.Stock = self.Stock_e.get()
        self.CP = self.CP_e.get()
        self.SP = self.SP_e.get()
        self.Vendor = self.Vendor_e.get()
        self.Vendor_PhoneNumber = self.Vendor_PhoneNumber_e.get()

        self.TotalCP = float(self.CP) * float(self.Stock)
        self.TotalSP = float(self.SP) * float(self.Stock)
        self.Assumed_profit = float(self.TotalSP - self.TotalCP)

        if self.Name =='' or self.Stock == '' or self.CP == '' or self.SP =='':
            tkinter.messagebox.showinfo("Provedor", "FAVOR PREENCHER TODOS OS CAMPOS!")
        else:
            sql = "INSERT INTO inventory (Name, Stock, CP, SP, Vendor, Vendor_PhoneNumber, TotalCP, TotalSP, Assumed_profit) VALUES(?,?,?,?,?,?,?,?,?)"
            c.execute(sql,(self.Name, self.Stock, self.CP, self.SP, self.Vendor, self.Vendor_PhoneNumber, self.TotalCP, self.TotalSP, self.Assumed_profit))
            conn.commit()

            self.textBox.insert(END, "\n\nCadastro" + str(self.Name) + "no banco de dados com o ID:" + str(ID))
            tkinter.messagebox.showinfo ("Provedor", "CADASTRO FEITO COM SUCESSO!")

    def clear_all(self, *args, **kwargs):
        num = ID + 1
        self.Name_e.delete(0,END)
        self.Stock_e.delete(0,END)
        self.CP_e.delete(0,END)
        self.SP_e.delete(0,END)
        self.Vendor_e.delete(0,END)
        self.Vendor_PhoneNumber_e.delete(0,END)


root = Tk()
b = Database(root)

root.geometry("1366x768+0+0")
root.title("FORMULARIO DE CADASTRO")
root.mainloop()

Error:

Error:
 Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\Cliente\AppData\Local\Programs\Python\Python38-32\lib\tkinter\__init__.py", line 1883, in __call__
    return self.func(*args)
  File "C:/TkinterVenda/Database/add_to_db.py", line 85, in get_items
    self.TotalCP = float(self.CP) * float(self.Stock)
ValueError: could not convert string to float: ''

[Yoriz]

What is it that you are entering into the entry that you are trying to convert to a float?

[SmukasPlays]

What is it that you are entering into the entry that you are trying to convert to a float?

CP and SP are the Cost Price and Sell Price

[Yoriz]

But whatever you are entering cannot be converted into a float

Python 3.7.6 (default, Jan  8 2020, 20:23:39) [MSC v.1916 64 bit (AMD64)] :: Anaconda, Inc. on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> float('')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float:
>>>  

what values have you typed into your entrys
print self.CP & self.Stock before attempting to convert them to a float, what values do they have?

[SmukasPlays]

But whatever you are entering cannot be converted into a float

Python 3.7.6 (default, Jan  8 2020, 20:23:39) [MSC v.1916 64 bit (AMD64)] :: Anaconda, Inc. on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> float('')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float:
>>>  

what values have you typed into your entrys
print self.CP & self.Stock before attempting to convert them to a float, what values do they have?

Sorry, I have expressed in a bad way these errors. It happens when I doesn't enter with one of these fields (CP or SP). When I don't fill them, it's expected to show a message box saying "PLEASE FILL ALL FIELDS" (POR FAVOR PREENCHA TODOS OS CAMPOS). When i fill everything, it almost works. Just the ID number doesn't change.

[Yoriz]

Move your conversions to the start of the else statement, so you are checking for valid input before trying to convert.

[SmukasPlays]

Move your conversions to the start of the else statement, so you are checking for valid input before trying to convert.

Oh, it was just it. Thank you very much!