Simple Cash Register -Python

Question

here it is my simple cash register app. It lacks some functionality ( class Payments should have more options like daily statements etc, class TillSettings needs more settings as well) but it does the job. Simple Cash Register and Stock Manager allows to add items to stock and then sell it and register total value of sales (very basic options). There is one bug I haven't fixed yet but that is a matter just of time. My question is do you have any advice for beginner in building 'bigger' apps. I mean that could be extended for multiple options, clerk id, manager privileges, refunds etc but have I started anywhere close to the right way? Any advice and critic will be appreciated. This is only one of the projects for me to learn so having my code seen and commented on by people who know how to do these things is important to me.

enter image description here

import tkinter as tk
import os, json
from typing import Any
from tkinter import DoubleVar, StringVar, ttk
from tkinter.constants import CENTER, END, NO
class Application(tk.Tk):
 def __init__(self, database: 'StockDatabase', settings: 'TillSettings', payments: 'Payments') -> None:
 super().__init__()
 self._db = database
 self._sett = settings
 self._pay = payments
 
 self.geometry('500x500')
 self.geometry('+100+100')
 self.title('Cash Register')
 self.iconbitmap('icon.ico')
 
 self.createButtons()
 self.createPurchaseList()
 self.createLabels()
 def createButtons(self) -> None:
 addToCart = ttk.Button(self, text='Add to basket', command=self.addToBasket)
 addToCart.place(x=10, y=10, width=90, height=50)
 
 stockManagment = ttk.Button(self, text='Manage Stock', command=self.manageStockWindow)
 stockManagment.place(x=10, y=430, width=90)
 
 exitButton = ttk.Button(self, text='EXIT', command= self.destroy)
 exitButton.place(x=10, y=460, width=90)
 
 paymentButton = ttk.Button(self, text='PAY', command=self.getPayment)
 paymentButton.place(x=390, y=420, height=70, width=90)
 def createPurchaseList(self) -> None:
 columns = ('#1', '#2', '#3', '#4')
 # set shopping list panel
 self.shoppingList = ttk.Treeview(self, columns=columns, show='headings', height=27, selectmode='browse')
 self.shoppingList.place(x=150, y=10, width=330, height=400)
 self.shoppingList.heading('#1', text='Product')
 self.shoppingList.heading('#2', text='#') # quantity
 self.shoppingList.heading('#3', text='#') # price per item
 self.shoppingList.heading('#4', text='Sum')
 self.shoppingList.column('#1', anchor=CENTER, stretch=NO, width=157)
 self.shoppingList.column('#2', anchor=CENTER, stretch=NO, width=50)
 self.shoppingList.column('#3', anchor=CENTER, stretch=NO, width=50)
 self.shoppingList.column('#4', anchor=CENTER, stretch=NO, width=70)
 # set scrollbar for shopping list
 scrollbar = ttk.Scrollbar(self, orient=tk.VERTICAL, command=self.shoppingList.yview)
 self.shoppingList.configure(yscrollcommand=scrollbar.set)
 scrollbar.place(x=481, y=10, height=400)
 def manageStockWindow(self) -> None:
 mngStockWin = tk.Toplevel()
 mngStockWin.geometry('350x600')
 mngStockWin.geometry('+150+100')
 mngStockWin.title('Stock Manager')
 mngStockWin.iconbitmap('icon.ico')
 def addNewItem() -> None:
 newItemWin = tk.Toplevel()
 newItemWin.geometry('300x200')
 newItemWin.geometry('+200+200')
 newItemWin.title('New Item Menu')
 newItemWin.iconbitmap('icon.ico')
 
 # set labels
 nameLabel = ttk.Label(newItemWin, text='Product:')
 nameLabel.place(x=10, y=10)
 priceLabel = ttk.Label(newItemWin, text='Price:')
 priceLabel.place(x=10, y=30)
 purchaseLabel = ttk.Label(newItemWin, text='Purchase Price:')
 purchaseLabel.place(x=10, y=50)
 quantityLabel = ttk.Label(newItemWin, text='Quantity:')
 quantityLabel.place(x=10, y=70)
 # set entry points
 tk.nameVar = StringVar(value='Product')
 nameEntry = ttk.Entry(newItemWin, textvariable=tk.nameVar, justify='right')
 nameEntry.place(x=150, y=10)
 
 tk.priceVar = DoubleVar(value=0.0)
 priceEntry = ttk.Entry(newItemWin, textvariable=tk.priceVar, justify='right')
 priceEntry.place(x=150, y=30)
 tk.purchaseVar = DoubleVar(value=0.0)
 purchaseEntry = ttk.Entry(newItemWin, textvariable=tk.purchaseVar, justify='right')
 purchaseEntry.place(x=150, y=50)
 tk.quantityVar = DoubleVar(value=0.0)
 quantityEntry = ttk.Entry(newItemWin, textvariable=tk.quantityVar, justify='right')
 quantityEntry.place(x=150, y=70)
 # window buttons
 cancelButton = ttk.Button(newItemWin, text='CANCEL', command=newItemWin.destroy)
 cancelButton.place(x=190, y=150, height=30)
 addButton = ttk.Button(newItemWin, text='ADD ITEM', command=lambda: [StockDatabase.addNewStockItem(self._db, [tk.nameVar.get(), 
 tk.priceVar.get(), 
 tk.purchaseVar.get(), 
 tk.quantityVar.get()]), 
 newItemWin.destroy(), 
 mngStockWin.destroy(), 
 self.manageStockWindow()])
 addButton.place(x=30, y=150, height=30)
 
 cancelButton = ttk.Button(mngStockWin, text='CANCEL', command=mngStockWin.destroy)
 cancelButton.place(x=250, y=550, height=30)
 addButton = ttk.Button(mngStockWin, text='ADD', command=addNewItem)
 addButton.place(x=10, y=550, height=30)
 
 
 # msw = Manage Stock Window
 mswColumns = ('#1', '#2', '#3', '#4')
 stockList = ttk.Treeview(mngStockWin, columns=mswColumns, show='headings', height=27, selectmode='browse')
 stockList.place(x=10, y=10, width=315, height=500)
 stockList.heading('#1', text='Product')
 stockList.heading('#2', text='Price')
 stockList.heading('#3', text='Purchase Price')
 stockList.heading('#4', text='Quantity')
 stockList.column('#1', anchor=CENTER, stretch=NO, width=133)
 stockList.column('#2', anchor=CENTER, stretch=NO, width=60)
 stockList.column('#3', anchor=CENTER, stretch=NO, width=60)
 stockList.column('#4', anchor=CENTER, stretch=NO, width=60)
 scrollbar = ttk.Scrollbar(mngStockWin, orient=tk.VERTICAL, command=self.shoppingList.yview)
 stockList.configure(yscrollcommand=scrollbar.set)
 scrollbar.place(x=325, y=10, height=500)
 # insert data to stock list
 for item in StockDatabase.loadData(self._db):
 stockList.insert('', tk.END, values=item)
 def deleteItem() -> None:
 # get choosen item
 currentItem = stockList.focus()
 itemInfo = stockList.item(currentItem)
 itemDetails = itemInfo["values"]
 
 # excepting index error if someone would press delete when stock list is empty
 try:
 # corrected for 'for' loop comparison. .focus() .item() returned all values as str
 correctedType = (itemDetails[0], float(itemDetails[1]), float(itemDetails[2]), float(itemDetails[3]))
 # delete item
 newData: list[Any] = []
 for item in StockDatabase.loadData(self._db):
 if item != correctedType:
 newData.append(item)
 StockDatabase.createNewStockFile(self._db)
 for item in newData:
 StockDatabase.addNewStockItem(self._db, item)
 # refresh stock list
 mngStockWin.destroy()
 self.manageStockWindow()
 except IndexError:
 pass
 # delete button
 deleteButton = ttk.Button(mngStockWin, text='DELETE', command=deleteItem)
 deleteButton.place(x=170, y=550, height=30)
 def amendItemDetails() -> None:
 amendWin = tk.Toplevel()
 amendWin.geometry('250x250')
 amendWin.geometry('+200+200')
 amendWin.title('Change details')
 amendWin.iconbitmap('icon.ico')
 questionLabel = ttk.Label(amendWin, text='What would you like to change?')
 questionLabel.place(x=10, y=10)
 itemOptions = ('Sale Price', 'Purchase Price', 'Stock Quantity')
 choice = StringVar()
 options = ttk.OptionMenu(amendWin,
 choice,
 itemOptions[0],
 *itemOptions)
 options.place(x=10, y=47)
 options.config(width=15)
 itemNewData = ttk.Label(amendWin, text='New Data:')
 itemNewData.place(x=10, y=90)
 newDataEntry = ttk.Entry(amendWin, justify='right')
 newDataEntry.place(x=10, y= 130)
 def acceptNewData(detailIndex: int, newDetail: Any) -> None:
 # get choosen item
 currentItem = stockList.focus()
 itemInfo = stockList.item(currentItem)
 itemDetails = itemInfo["values"]
 print(itemDetails)
 # corrected for 'for' loop comparison. .focus() .item() returned all values as str
 correctedType = (itemDetails[0], float(itemDetails[1]), float(itemDetails[2]), float(itemDetails[3]))
 print(correctedType)
 newData: list[Any] = []
 for item in StockDatabase.loadData(self._db):
 if item != correctedType:
 print(item)
 newData.append(item)
 
 # append changed item
 itemDetails[detailIndex] = float(newDetail)
 # type adjustment as floats were turned into strings
 itemDetails = (itemDetails[0], float(itemDetails[1]), float(itemDetails[2]), float(itemDetails[3]))
 newData.append(itemDetails)
 print(itemDetails)
 print(correctedType)
 StockDatabase.createNewStockFile(self._db)
 # write to database
 for item in newData:
 StockDatabase.addNewStockItem(self._db, item)
 
 # destroy window after changing details
 amendWin.destroy()
 # refresh stock list
 mngStockWin.destroy()
 self.manageStockWindow()
 
 okButton = ttk.Button(amendWin, text='UPDATE', command=lambda: acceptNewData(itemOptions.index(choice.get()) + 1, newDataEntry.get()))
 okButton.place(x=60, y=200)
 cancelButton = ttk.Button(amendWin, text='CANCEL', command=amendWin.destroy)
 cancelButton.place(x=150, y=200)
 amendButton = ttk.Button(mngStockWin, text='CHANGE', command=amendItemDetails)
 amendButton.place(x=90, y=550, height=30)
 
 def addToBasket(self) -> None:
 basketWin = tk.Toplevel()
 basketWin.geometry('250x200')
 basketWin.geometry('+200+200')
 basketWin.title('Add Item to Basket')
 basketWin.iconbitmap('icon.ico')
 itemLabel = ttk.Label(basketWin, text='Item:')
 itemLabel.place(x=10, y=10)
 quantityLabel = ttk.Label(basketWin, text='Quantity:')
 quantityLabel.place(x=10, y=70)
 availableLAbel = ttk.Label(basketWin, text='Available:')
 availableLAbel.place(x=10, y=110)
 # load options from available stock
 def getOptions() -> list[str]:
 choice: list[str] = []
 for item in StockDatabase.loadData(self._db):
 choice.append(item[0])
 if len(choice) == 0:
 choice = ['Nothing in stock']
 return choice
 tk.choosenItem = StringVar()
 options = ttk.OptionMenu(basketWin,
 tk.choosenItem,
 getOptions()[0],
 *getOptions())
 options.place(x=120, y=10)
 options.config(width=15)
 # get maximum quantity of item from stock database
 def getMaxQuantity(item: str) -> float:
 for product in StockDatabase.loadData(self._db):
 if product[0] == item:
 return float(product[3])
 tk.quantityVar = DoubleVar(value=getMaxQuantity(tk.choosenItem.get()))
 quantityAmountLabel = ttk.Label(basketWin, textvariable=tk.quantityVar, justify='right', background='lightgrey')
 quantityAmountLabel.place(x=215, y=110)
 tk.entryVar = DoubleVar()
 quantityEntry = ttk.Entry(basketWin, textvariable=tk.entryVar, justify='right')
 quantityEntry.place(x=120, y=70, width=120)
 cancelButton = ttk.Button(basketWin, text='CANCEL', command=basketWin.destroy)
 cancelButton.place(x=140, y=150)
 # insert maximum available stock in quantity label, update everytime different option from option menu is choosen
 # x, y, z just to pass argument to callback function, as required by tkinter. otherwise= error
 def updateQuantity(x: Any, y: Any, z: Any) -> None:
 tk.quantityVar = DoubleVar(value=getMaxQuantity(tk.choosenItem.get()))
 quantityAmountLabel['textvariable'] = tk.quantityVar
 tk.choosenItem.trace_add('write', updateQuantity)
 '''NEED TO WORK ON THIS PART
 EVERYTHING IS WORKING FINE, BUT WHILE ADDING SAME ITEM MULTIPLE TIMES
 WHEN IT COMES TO PAYMENT TIME stock_data.json IS NOT UPDATED CORRECTLY.
 NEED TO FIND THE WAY TO CONSOLIDATE ITEMS IN THE shoppingList'''
 # create item for the shopping list, calculate sum for product (quantity * price)
 def addToShoppingList(item: str, quantity: float) -> None:
 productToAdd: list[Any] = []
 productToAdd.append(item)
 # excepting TypeError if someone will try to add items when stock_data is empty
 try:
 # ensure it can't be added more than in the stock
 if quantity >= getMaxQuantity(tk.choosenItem.get()):
 productToAdd.append(getMaxQuantity(tk.choosenItem.get()))
 else:
 productToAdd.append(quantity)
 for product in StockDatabase.loadData(self._db):
 if product[0] == item:
 productToAdd.append(product[1])
 total = productToAdd[1] * productToAdd[2]
 productToAdd.append(total)
 self.shoppingList.insert('', tk.END, values=productToAdd)
 except TypeError:
 pass
 addButton = ttk.Button(basketWin, text='ADD', command=lambda: addToShoppingList(tk.choosenItem.get(), tk.entryVar.get()))
 addButton.place(x=30, y=150)
 def createLabels(self) -> None:
 totalLabel = ttk.Label(self, text='TOTAL:')
 totalLabel.place(x=150, y=420)
 taxLabel = ttk.Label(self, text='TAX:')
 taxLabel.place(x=150, y=445)
 toPayLabel = ttk.Label(self, text='TOTAL TO PAY:')
 toPayLabel.place(x=150, y=470)
 def calculateTotal() -> float:
 total: float = 0.0
 for child in self.shoppingList.get_children():
 total += float(self.shoppingList.item(child, 'values')[3])
 return total
 def getTaxValue() -> float:
 for item in TillSettings.loadSettings(self._sett):
 for key, value in item.items():
 if key == 'sales tax':
 return value
 return 0.0
 # just a basic tax calculation for training purposes
 def calculateTax(amount: float) -> float:
 return round((amount / 100) * getTaxValue(), 2)
 self.totalVar = DoubleVar(value=calculateTotal())
 totalValue = ttk.Label(self, textvariable=self.totalVar, background='lightgrey')
 totalValue.place(x=330, y=420)
 self.taxVar = DoubleVar(value=calculateTax(self.totalVar.get()))
 taxValue = ttk.Label(self, textvariable=self.taxVar, background='lightgrey')
 taxValue.place(x=330, y=445)
 self.toPayVar = DoubleVar(value=self.taxVar.get() + self.totalVar.get())
 toPayValue = ttk.Label(self, textvariable=self.toPayVar, background='lightgrey')
 toPayValue.place(x=330, y=470)
 def updateTotals() -> None:
 self.totalVar = DoubleVar(value=calculateTotal())
 self.taxVar = DoubleVar(value=calculateTax(self.totalVar.get()))
 self.toPayVar = DoubleVar(value=self.taxVar.get() + self.totalVar.get())
 totalValue = ttk.Label(self, textvariable=self.totalVar, background='lightgrey')
 totalValue.place(x=330, y=420)
 taxValue = ttk.Label(self, textvariable=self.taxVar, background='lightgrey')
 taxValue.place(x=330, y=445)
 toPayValue = ttk.Label(self, textvariable=self.toPayVar, background='lightgrey')
 toPayValue.place(x=330, y=470)
 self.after(1000, updateTotals)
 updateTotals()
 def getPayment(self) -> None:
 # update total payment
 Payments.updateTotalPayments(self._pay, self.toPayVar.get())
 # update stock values
 newData: list[Any] = []
 updatedData: list[Any] = []
 for item in StockDatabase.loadData(self._db):
 item = list(item)
 for child in self.shoppingList.get_children():
 if self.shoppingList.item(child, 'values')[0] == item[0]:
 item[3] -= float(self.shoppingList.item(child, 'values')[1])
 updatedData.append(list(item)) 
 
 # get names of bought products
 compareList: list[str] = []
 for item in updatedData:
 compareList.append(item[0])
 print(compareList)
 print(updatedData)
 # append new data with not bought products
 for item in StockDatabase.loadData(self._db):
 if item[0] not in compareList:
 newData.append(list(item))
 # append new data with bought products with new values
 for item in updatedData:
 newData.append(item)
 print(newData)
 # write to file procedure
 StockDatabase.createNewStockFile(self._db)
 for item in newData:
 StockDatabase.addNewStockItem(self._db, item)
 # clear shopping list after successful purchase
 self.shoppingList.delete(*self.shoppingList.get_children())
 
class StockDatabase:
 def __init__(self, dataFile: str) -> None:
 self._stockFile = dataFile
 # check for stock data file existence
 if os.path.isfile(self._stockFile) == True and os.stat(self._stockFile).st_size != 0:
 pass
 else:
 self.createNewStockFile()
 def createNewStockFile(self) -> None:
 with open(self._stockFile, 'w') as f:
 writeData: dict[str, list[Any]] = {"stock": []}
 json.dump(writeData, f, indent=4)
 
 def addNewStockItem(self, newItem: list[Any]):
 item = {
 "item": newItem[0],
 "sale price": newItem[1],
 "purchase price": newItem[2],
 "stock quantity": newItem[3]
 }
 with open(self._stockFile, 'r') as f:
 data = json.load(f)
 data["stock"].append(item)
 with open(self._stockFile, 'w') as f:
 json.dump(data, f, indent=4)
 def loadData(self) -> list[Any]:
 stockItem = []
 with open(self._stockFile, 'r') as f:
 data = json.load(f)
 for itemData in data["stock"]:
 item: str = itemData["item"]
 salePrice: float = itemData["sale price"]
 purchasePrice: float = itemData["purchase price"]
 stockQuantity: float = itemData["stock quantity"]
 stockItem.append((item, salePrice, purchasePrice, stockQuantity))
 return stockItem
class TillSettings:
 def __init__(self, dataFile: str) -> None:
 self._settFile = dataFile
 # check for settings file existence
 if os.path.isfile(self._settFile) == True and os.stat(self._settFile).st_size != 0:
 pass
 else:
 self.createNewSettingsFile()
 def createNewSettingsFile(self) -> None:
 with open(self._settFile, 'w') as f:
 writeData = {"settings" : [{
 "sales tax": 0
 }]
 }
 json.dump(writeData, f, indent=4)
 
 def loadSettings(self) -> list[Any]:
 settings: list[Any] = []
 with open(self._settFile, 'r') as f:
 data = json.load(f)
 for item in data["settings"]:
 settings.append(item)
 return settings
class Payments:
 def __init__(self, paymentFile: str) -> None:
 self._paymentFile = paymentFile
 # check for file existence
 if os.path.isfile(self._paymentFile) == True and os.stat(self._paymentFile).st_size != 0:
 pass
 else:
 self.createNewPaymentFile()
 
 def createNewPaymentFile(self) -> None:
 with open(self._paymentFile, 'w') as f:
 writeData = {"Total Payments": 0}
 json.dump(writeData, f, indent=4)
 
 def updateTotalPayments(self, payment: float):
 with open(self._paymentFile, 'r') as f:
 data = json.load(f)
 data["Total Payments"] += payment
 with open(self._paymentFile, 'w') as f:
 json.dump(data, f, indent=4)
if __name__ == '__main__':
 _stockFIle = f'{os.path.dirname(__file__)}\\stock_data.json'
 _settFile = f'{os.path.dirname(__file__)}\\settings.json'
 _paymentFile = f'{os.path.dirname(__file__)}\\payments.json'
 db = StockDatabase(_stockFIle)
 sett = TillSettings(_settFile)
 pay = Payments(_paymentFile)
 Application(database= db, settings= sett, payments= pay).mainloop()

• Was': I can't run the code because list[Any] in line 458 causes error, is it because it's written in old python?
• hjpotter92: @WalidSiddik list[Any] is the newer syntax.
• Was': @hjpotter92. It says TypeError: 'type' object is not subscriptable (python 3.8)
• Jakub: When do you get that error? The only one error I can get atm is when I try to input str in place where float should be, but that is easy to fix.
• hjpotter92: @WalidSiddik python.org/dev/peps/pep-0585 it was implemented in 3.9+

Answer 1

Violation of PEP8

According to PEP8,

• Imports should be on seperate lines.
• Surround top-level function and class definitions with two blank lines.
• Method definitions inside a class are surrounded by a single blank line.
• Variables and function names should be snake_case.

My thoughts

• You should create seperate files for GUI and Data Handling part. Currently your code is around 550 lines which makes it hard to navigate over.

• I do not know why you have done this tk.priceVar = .... Better make it self.prive_var.

• You have justified all the entries to the right. This causes some unwanted behaviour.

Your GUI part is very well done. But I would like some additions -

• Currently one can not remove an item from the basket.
• Your 2nd and 3rd columns are named #. Would be better if renamed.

Waiting to see the other parts of the project in action. Happy Coding!

• Jakub: I was always naming my_functions rather than myFunction but been told that way it looks more "proper", will stick to my_function as I prefer it anyway. Yes delete but for shoppingList will be added and some more, just wasn't sure if my approach to build this app right. Need to test adding window again as I didn't have that issue. Splitting the code in to different files would make a lot of sense, will need to do it. Thank you very much for your time.
• Jakub: Remove button is added now, the issue from your screenshot is also fixed. A few more things and I will re-upload the code. Waiting for one of my friends to bring me a scanner and till draw, so may be able to add barcode reading and a function to open the draw when payment is done.
• Random_Pythoneer59: All the best!!!