main.py

from datetime import datetime

def main() -> None: 
    # Assume that the "End of business day" is after 8pm, Mon-Sun

    role=""
    auto=True
    # Access control
    option_ls={
            "admin": ["insert_item", "update_item", "delete_item", "stock_taking", 
                      "view_replenish_list", "stock_replenishment", "search_items", "add_user"],
            "inventory-checker": ["stock_taking", "search_items"],
            "purchaser": ["view_replenish_list", "stock_replenishment", "search_items"]
            }
    # Welcome message
    print("\nWelcome to ▶ GROCERY STORE INVENTORY SYSTEM ◀\n")
    while True:
        # Authentication
        if not role:
            role=user_authentication()
            auto=True
        
        if auto: # This should only do one time for each login
            # If user is inventory checker and the time is end of business day
            if role=="inventory-checker" and int(datetime.now().strftime("%H"))>=20:
                print("\nYou are inventory checker and now is the end of business day")
                print("ALERT: Please perform stock-taking")
                stock_taking(role)

            # If user is purchaser and the time is end of business day
            elif role=="purchaser" and int(datetime.now().strftime("%H"))>=20:
                print("\nYou are purchaser and now is the end of business day")
                print("ALERT: Please view replenish list")
                view_replenish_list(role)
            auto=False 

        try:
            # Display list options
            print("\nYou are now at: ▶ Main Menu ◀\n")
            if role in option_ls.keys():
                for ind in range(len(option_ls[role])):
                    option=option_ls[role][ind].split("(")[0].replace("_", " ").title()
                    print(f"Type {ind+1} to {option}")
            # Invalid role
            else:
                raise Exception("Invalid role!")

            # Display logout and exit options
            print("\nType 'e' to exit the system\nType 'l' to logout")
            # User input
            inp=input("\nPlease enter your option: ")

            # Exit
            if inp.strip()=="e":
                print("\nEXIT GROCERY STORE INVENTORY SYSTEM")
                exit()
            # Logout
            elif inp.strip()=="l":
                role=""
                print("\nLog Out")
                continue
            # Execute option's function
            elif inp.strip().isdecimal() and 0<int(inp)<=len(option_ls[role]):
                eval(option_ls[role][int(inp)-1]+"(role)")
            # Error
            else:
                raise Exception("Invalid option!")
            
        # Display error
        except Exception as e:
            print("ERROR:", e)

def inventory_data_list() -> list:
    file_dir="inventory.txt"
    # Open file and save each line into a list
    with open(file_dir, "r") as inventory_file:
        data_list=inventory_file.readlines()
    
    # Convert to 2D list
    for ind, data in enumerate(data_list):
        data_list[ind]=data.rstrip().split("\t")
    return data_list

def user_authentication() -> str:
    # Assume "userdata.txt" is placed in the same directory as code file
    # Assume that credentials in "userdata.txt" are correct

    # Initialize
    filename="userdata.txt"
    credentials=username=password=""
    print("LOGIN AUTHENTICATION\nPlease login using your username and password.")
    print("WARNING: username and password are case-sensitive")
    while True:
        # Opening file and taking credentials from file
        with open(filename, 'r') as file:
            credentials = file.readlines()

        for ind, data in enumerate(credentials):
            credentials[ind] = data.rstrip().split("\t")

        # Asking for user input
        username = input("Enter your username: ").strip()
        password = input("Enter your password: ").strip()
        for line in credentials:
            if line[1] == username and line[2] == password:
                role = line[3]
                print("Authentication successful. User is a(n)", role)
                return role
        else:
            print("Authentication failed! Incorrect password or username, please login again.")

def add_user(role:str) -> None: 
    # Assume that username should be unique
    # Assume user's password must be minimum 8 in length
    # Assume there are only 3 roles that will use the system, which are "admin", "inventory-checker" and "purchaser" 
    # Assume that "userdata.txt" is placed in the same directory as this file

    # Initialization
    file_dir="userdata.txt"
    user_info=""
    access_allowed=("admin",) # Only admin can add new user

    # Welcome message
    print("\nYou are now at: ▶ Add New User (Admin only) ◀\nTo add a new user, you need to specify username, password and user type. Please type these data separated by comma(,)\nMinimum 8 characters required for password.\nWARNING: username and password are both case-sensitive and space-sensitive!\n")
    # Validate user type
    if role not in access_allowed:
        print("REJECTED: You have no permission to access this, please login again!")

    # If user is admin
    else:
        user_type_allowed=("admin", "inventory-checker", "purchaser") # 3 types of user allowed to input

        # Repeat asking user to input new user's details until request to exit
        while True:
            errors=[]
            #Guide user to input
            print("Format: <username>,<password>,<user_type>\nExample input: Ali,1234A@bc,purchaser\nTo return back to main menu, type 'q'\n")

            # Get new user's info 
            user_info=(input("Please enter new user's info: ").rstrip()).split(",")

            try:
                # Data validation
                # If user choose to exit
                if len(user_info)==1 and "q" in user_info:
                    break

                # If not 2 commas in the input
                if len(user_info) !=3:
                    raise Exception("Please input username, password and user type!")
                
                # If username is empty
                if len(user_info[0].strip())<1:
                    errors.append("Username cannot be empty!")
                
                # If password length not exceed 8
                if len(user_info[1])<8 :
                    errors.append("Password length must more than or equal to 8!")
                
                # If user type is invalid
                if user_info[2].lower().strip() not in user_type_allowed:
                    errors.append("Invalid user type!")

                if errors:
                    raise Exception(errors)

                # After data validation pass
                # Confirm with user before adding the data into txt
                username, password, user_type=user_info
                print(f"\n\nNew user info\nusername: {username.strip()}\t|\tpassword: {password}\t|\tuser_type: {user_type.lower().strip()}")
                print("\nType 'y' to confirm, or any other characters to discard")

                # If user confirmed, add data
                if input("Confirm? (y): ").lower().strip() == "y":
                    row_num=sum(1 for x in open(file_dir, "r")) # Get row number

                    # Open file and append userdata
                    with open(file_dir, "a+") as credential_file:
                        # Reject if the user already exists
                        credential_file.seek(0)
                        if any([line for line in credential_file.readlines() if username.strip() == line.split("\t", 2)[1].strip()]):
                            raise Exception("User already exists!")
                        
                        # If user not exist
                        else:
                            credential_file.write(f"{row_num+1}\t{username.strip()}\t{password}\t{user_type.lower().strip()}\n")
                            print("\nAdded successfully!\n\n")

                    # Ask user if want to add new user or exit
                    print("Type 'y' to add another user, other characters to quit. ")
                    if input("Add another user or exit?(y)").lower().strip() =="y": # If user request to continue adding new user
                        print("\n\nYou are now at: ▶ Add New User (Admin only) ◀")
                        continue
                    else: # If user request to exit
                        break
                
                # If user choose to discard data
                else:
                    print("\nDISCARDED\n")
                    continue 

            # Error handler
            except Exception as e:
                user_info="" # user info reset if any error is found
                print("\n\nERROR:",e, "\n")
    
    # Code below will be run if user choose to exit and the loop breaks
    print("\nEXIT add user function\n")

def insert_item(role:str) -> None:
    # Assume item code's format is 5-digit number and unique
    # Assume that "inventory.txt" is placed in the same directory as this file
    # Assume that price must be in 2 decimal format

    print("\nYou are now at: ▶ Insert Items (Admin only) ◀")
    file_dir="inventory.txt"
    # Initialize
    product_info="" # This variable is to accept input
    datalist = [] # This list is to store data temporarily
    codelist=[] # This list is to store item codes in the temporary datalist
    # Only the admin can access
    access_allowed=("admin",) # Only admin can access

    # While loop is used so user can bulk import items
    while True:   
        if role not in access_allowed: # Check permission
            print("REJECTED: You have no permission to access this, please login again!")
            break # Return to main menu
            
        try:
            # Collect the item codes into a list
            if datalist:
                codelist=[code[:5] for code in datalist]
            print('\nPlease enter all the information based on the format below\nFORMAT: <Code>,<Description>,<Category>,<Unit>,<Price>,<Quantity>,<Minimum>')
            print("EXAMPLE: 10000,Milk 1L,Dairy,box,7.00,30,35\n")
            print("Type 'q' to return back to main menu")
            product_info=input('Please enter all the information of this product: ').split(",")

            if len(product_info)==1 and "q" in product_info: # If user choose to exit
                break

            # Check if 7 details in the input
            if len(product_info) !=7:
                raise Exception ("Invalid input format! Please enter according to format.")

            # Check if item code is 5 digit number
            if not product_info[0].strip().isdecimal() or not len(product_info[0].strip())==5:
                raise Exception ("Please enter a 5 digit number for item code.")
            else:
                # Check if item code is unique
                with open(file_dir, 'r') as inventoryfile:
                    for line in inventoryfile.readlines():
                        if product_info[0] in line[:5] or product_info[0] in codelist: # Check both file and datalist if the item code exists
                            raise Exception ("The item code must be unique")
            
            if not product_info[1].strip(): # Check description if empty
                raise Exception ("Description is empty, please enter the description for this product.")
            
            if not product_info[2].strip(): # Check category if empty
                raise Exception ("Cateogry is empty, please enter the category for this product")
            
            if not product_info[3].strip(): # Check Unit if empty
                raise Exception ("Unit is empty, please enter the Unit of this product.")
            
            # Try convert Price to 2 decimal, or throw error
            try: 
                product_info[4]='%.2f' % float(product_info[4].strip())
            except:
                raise Exception ("Price must be number.")
                
            #Check if quanity is positive integer
            if not product_info[5].strip().isdecimal():
                raise Exception ("Quantity must be positive integer.")
            
            #Check if minimum is positive integer
            if not product_info[6].strip().isdecimal():
                raise Exception ("Minimum must be positive integer.")

            # Save temporarily in a list
            datalist.append("\t".join(product_info)+"\n")
            
            if input("Type 'y' to continue adding new item, or any other character to submit: ") =='y': 
                continue # If user want to continue add other items, loop again
            else: # If user doesn't want to add other items
                with open(file_dir, 'a') as inventoryfile: # Open file in append mode
                    inventoryfile.writelines(datalist)
                print("Item(s) added successfully")
                break # Return back to main menu after finish adding items

        except Exception as e:
            print("\nERROR:",e)

    print("\nEXIT insert item function")

def update_item(role:str) -> None:
    # Assume item code's format is 5-digit numbers and unique
    # Assume that "inventory.txt" is placed in the same directory as this file
    # Assume that price must be in 2 decimal format
    # Assume that the data entered accurately reflects the actual situation
    # Validation on the format of the data only, not the reliability

    # Initialization
    file_dir="inventory.txt" # Locate the txt file directory
    access_allowed=("admin",) # Only admin can add new user
    code=change=""
    d={
        "1": "Item code (MUST be 5 digits)",
        "2": "Description",
        "3": "Category",
        "4": "Unit",
        "5": "Price", 
        "6": "Quantity",
        "7": "Minimum (Threshold)"
    }
    
    print("\nYou are now at: ▶ Update Items (Admin only) ◀\n")

    # Below will be repeated until user requests to exit
    while True:
        data_ls=[]
        code_ls=[]
        #check if user is admin
        if role not in access_allowed:
            print("REJECTED: You have no permission to access this, please login again!")
            break
        else:
            # Get all records out from txt file
            with open(file_dir, "r") as inventory_file:
                # Display records from txt file in a neat format
                print("{:10} {:20} {:15} {:10} {:10} {:10} {:10}".format(*["Code", "Description", "Category", "Unit", "Price", "Quantity", "Minimum (Threshold)"]))
                print("---"*35)
                for line in inventory_file:
                    print("{:10} {:20} {:15} {:10} {:10}\t{:10}\t{:10}".format(*(line.strip().split("\t")))) # Specify field size for each column
                
                # Save each line into a list
                inventory_file.seek(0)
                data_ls=inventory_file.readlines()

            # Convert to 2D list
            for ind, data in enumerate(data_ls):
                data_ls[ind]=data.rstrip().split("\t")
            # Save item code into a new list
            for line in data_ls:
                code_ls.append(line[0])

            try:
                print("\nAbove are the existing records\n\ntype 'q' to return back to main menu. ")

                #Request to input item code only when it's empty
                if not code:
                    code=input("Specify the item's code which you would like to update: ").strip()

                # If user choose to quit
                if code=="q":
                    break
                # Check if the input item code exist
                if code not in code_ls:
                    code=""
                    raise Exception("The item code is not found! ")

                # Request user to choose what to update for the item code's row
                print("\nWhat do you wish to update?")
                for key, col in d.items():
                    print(f"\t\tType {key} for {col}")
                print("""
                Type b to go back item list
                Type q to go back main menu\n
                """)
                print(f"You're now updating - {code}")
                change=input("Your option: ").strip()

                # Check if user want to quit or go back to main menu
                if not change.isdecimal():
                    if change=="b":
                        code="" # Reset item code to empty
                        print("\nBACK to item list\n")
                        continue
                    elif change=="q":
                        break
                    else:
                        raise Exception("Invalid Option!\n")

                # Check if option is valid
                elif int(change) not in range(1,8):
                    raise Exception("Invalid option!\n")
                
                # Locate the element to change
                row=code_ls.index(code)
                column=int(change)

                print(f"\n\nYou're now changing the item code: {code}, for its {d[change]}")
                print("[Enter 'b' to go back item list]")
                new_value=input("New value: ").strip()
                
                if new_value != "b":
                    # Data validation
                    if change=="1": # If request to change item code
                        if new_value in code_ls: # Code must be unique
                            raise Exception("Item code must be unique!\nThe new Code is either the same with the previous, or conflicts with other items' code.\n")
                        elif len(new_value) != 5 or not new_value.isdecimal(): # Code must contain 5 digits
                            raise Exception("Item code must be 5 digits!\n")
                        code=new_value
                    elif change in ["2", "3", "4"]: # If request to change description/category/unit
                        if not new_value.strip(): # Description cannot be changed to empty
                            raise Exception(f"{d[change]} cannot be empty!\n")
                    elif change in ["5", "6", "7"]: # If request to change Price/Quantity/Minimum
                        # Price/Quantity/Minimum must be number
                        try:
                            float(new_value)
                        except:
                            raise Exception(f"{d[change]} must be a number! \n")
                        
                        # Price will be converted to 2 decimal automatically
                        if change=="5":
                            new_value="%.2f" % float(new_value)
                        # Quantity and Minimum must be integer
                        else:
                            try:
                                new_value=int(new_value)
                            except: # Error if user input decimal
                                raise Exception(f"{d[change]} must be integer! \n")

                        
                    # If pass all check, change the value in the list        
                    data_ls[row][column-1]=str(new_value)
                    
                    # Update the changes with the list
                    with open(file_dir, "w") as inventory_file:
                        for row in data_ls:
                            if data_ls.index(row) != 0: # After writing each row, break line
                                inventory_file.write("\n")
                            for column in row: # Use TAB to separate columns
                                inventory_file.write(str(column)+"\t")
                        print("\nUPDATED SUCESSFULLY\n")
                    
                    # Ask if user want to continue updating the same item code or new item code
                    if input(f"Type 'y' to continue updating other details for {code},\nor any other characters to switch: ").strip().lower()=='y':
                        print("\nYou are now at: ▶ Update Items (Admin only) ◀\n")
                        continue
                    else:
                        print("\nYou are now at: ▶ Update Items (Admin only) ◀\n")
                        code="" # Reset item code to empty
                        continue
                else:
                    print("\nBACK to item list\n")

            # Error handler
            except Exception as e:
                print("\n\nERROR:",e, "\n") # Display error message
                continue
    print("\nEXIT update item function")

def delete_item(role:str) -> None:
    # Assume item code's format is 5-digit numbers and unique
    # Assume "inventory.txt" is placed in the same directory as code file
    # Assume that only item code can be accepted as input

    # Initialization
    file_dir = "inventory.txt"
    access_allowed = ["admin"] #Only admins allowed to access this function
    code = ""

    while True:
        data_ls = []
        code_ls = []

        # Access check
        if role not in access_allowed: 
            print("You do not have permissions to access this. Please login again.")
            break
        else:
            # Items display and formatting
            print("You are now at: ▶ Delete Item (Admin only) ◀\n")
            with open(file_dir, "r") as inventory_file:
                print("{:10} {:20} {:15} {:10} {:10} {:10} {:10}".format(*["Code", "Description", "Category", "Unit", "Price", "Quantity", "Minimum (Threshold)"]))
                print("---"*35)
                for line in inventory_file:
                    print(" {:10} {:20} {:15} {:10} {:10}\t{:10}\t{:10}".format(*(line.strip().split("\t"))))

                inventory_file.seek(0)
                data_ls = inventory_file.readlines()
            
            # Convert to 2D list
            for ind, data in enumerate(data_ls):
                data_ls[ind] = data.rstrip().split("\t")
            # Collect item codes
            for line in data_ls:
                code_ls.append(line[0])
            
            try:

                # Displaying available actions
                print("\nAbove are existing records\n\nType 'q' to return back to main menu. ")
                
                code = input("Which item would you like to delete? (Input item code): ").strip()
                if code == "q":
                    break
                if code not in code_ls:
                    code = ""
                    raise Exception("This item is not found. ")
                
                # Confirmation for deletion and deletion process
                if input(f"\nType 'y' to confirm, or any other characters to discard\nDelete {code}?(y): ").lower().strip() == "y":
                    new_rows = []
                    with open(file_dir, "w") as inventory_file:
                        for row in data_ls:
                            if row[0] == code:
                                continue
                            new_rows.append(row)
                        for row in new_rows:
                            inventory_file.write("\t".join(row) + "\n")
            
                    # Deletion completed
                    print("\nItem with code {} has been successfully deleted.\n".format(code))
                    code = ""
                    print("Type 'y' to delete another item, other characters to quit. ")
                    if input("Delete another item (y) or exit? ").lower().strip() =="y": 
                        print("\n\nYou are now at: ▶ Delete Item (Admin only) ◀")
                        continue
                    else: 
                        break
                else:
                    print("\nDISCARDED\n")
                    continue
            
            # Error handler
            except Exception as e:
                print("\n\nERROR:",e, "\n")
                continue
    print("\nEXIT delete item function")

def stock_taking(role:str) -> None:
    # Assume item code's format is 5-digit numbers and unique
    # Assume that "inventory.txt" is placed in the same directory as this file
    # Assume only item code can be accepted as input 

    #Initialize
    file_dir="inventory.txt" #Locates text file directory
    access_allowed=("admin","inventory-checker") # Only admin and inventory-checker can perform stock-taking
    data_ls=[]
    updated_data_ls=[]

    #Welcome message
    print("\nYou are now at: ▶ Stock Taking ◀\n")
    
    # Validate user type
    while True: 
        if role not in access_allowed: #check if user is admin
            print("REJECTED: You have no permission to access this, please login again!")
            break 
        try:
            # Get item 2D list
            data_ls=inventory_data_list()

            # Display existing inventory
            print("Below are the existing inventory:")
            print("{:10} {:20}".format(*["Code", "Description"]))
            for row in data_ls:
                print("{:10} {:20}".format(*[row[0], row[1]]))

            print("\nTo check the stock, first you need to enter an item code.")
            print("Type 'q' to go back to main menu.")

            ItemCode=input("\nPlease enter the item code: ").strip() #input 5 digit item code

            #If user wants to go back to main menu
            if ItemCode=="q":
                break #returns to main menu
            
            #checks for the specific row in the txt file
            for row in range(len(data_ls)): 
                if data_ls[row][0]==ItemCode: #check if input is in txt file 
                    print(f"Quantity for item code {ItemCode} is {data_ls[row][5]}") #prints the specific quantity for the item code that 
                    
                    #Ask user if quantity needs to be changed
                    QuantityChange = input("\nType 'y' to change the quantity: ").strip()
                    if QuantityChange == "y": #check if input is 'y' to change quantity
                        NewQuantity = input(f"Please enter new quantity for item code {ItemCode}: ").strip() 

                        #check if input is a positive integer
                        if not NewQuantity.isdecimal():
                            raise Exception("Quantity must be positive integer") 
                        data_ls[row][5] = NewQuantity

                        updated_data_ls=["\t".join(ele)+"\n" for ele in data_ls] # Convert 2D list to 1D list

                        # Updates the new quantity to the specific item code in the txt file
                        with open(file_dir, "w") as inventory_file:
                            inventory_file.writelines(updated_data_ls) 
                        print(f"\nSUCCESS: Quantity for item code {ItemCode} has been updated to {NewQuantity}\n")
                        break #returns to item code selection after made changes to quantity in file
                    else:
                        print("No change")
                        break #returns back to item code selection
            else: # If can't find the input item code until the end of file
                raise Exception("Item code not exists") 
        except Exception as e:
            print("\nERROR:",e)

    print("EXIT Stock-taking")

def stock_replenishment(role:str) -> None:
    # Assume item code's format is 5-digit numbers and unique
    # Assume that "inventory.txt" is placed in the same directory as this file
    # Assume only item code can be accepted as input 

    #Initialize
    file_dir="inventory.txt" #Locates text file directory
    access_allowed=("admin","purchaser") # Only admin and purchaser can perform stock-replenishment
    data_ls=[]
    updated_data_ls=[]

    #Welcome message
    print("\nYou are now at: ▶ Stock Replenishment ◀\n")
    
     # Validate user type
    while True: 
        if role not in access_allowed: #check if user is admin
            print("REJECTED: You have no permission to access this, please login again!")
            break 
        try:
            # Get item 2D list
            data_ls=inventory_data_list()

            # Display existing inventory
            print("Below are the existing inventory:")
            print("{:10} {:20}".format(*["Code", "Description"]))
            for row in data_ls:
                print("{:10} {:20}".format(*[row[0], row[1]]))

            print("\nTo add the stock, first you need to enter an item code.")
            print("Type 'q' to go back to main menu.")

            ItemCode=input("\nPlease enter the item code: ").strip() # input 5 digit item code

            #If user wants to go back to main menu
            if ItemCode=="q":
                break # returns to main menu
            
            #checks for the specific row in the txt file
            for row in range(len(data_ls)): 
                if data_ls[row][0]==ItemCode: #check if input is in txt file 
                    print(f"Quantity for item code {ItemCode} is {data_ls[row][5]}") #prints the specific quantity for the item code that 
                    
                    print("\nType 'b' to go back")
                    QuantityIncrease = input(f"Please enter quantity to add to current amount for item code {ItemCode}: ").strip() 

                    if QuantityIncrease=="b":
                        print("No change") 
                        break # return to item code selection
                    #check if input is a positive integer
                    if not QuantityIncrease.isdecimal():
                        raise Exception("Quantity must be positive integer") 
                    data_ls[row][5] = str(int(data_ls[row][5])+int(QuantityIncrease))

                    updated_data_ls=["\t".join(ele)+"\n" for ele in data_ls] # Convert 2D list to 1D list

                    # Updates the new quantity to the specific item code in the txt file
                    with open(file_dir, "w") as inventory_file:
                        inventory_file.writelines(updated_data_ls) 
                    print(f"\nSUCCESS: Quantity for item code {ItemCode} has been updated to {data_ls[row][5]}\n")
                    break # return to item code selection after made changes to quantity in file
                    
            else: # If can't find the input item code until the end of file
                raise Exception("Item code not exists") 
        except Exception as e:
            print("\nERROR:",e)

    print("EXIT Stock-replenmishment")

def view_replenish_list(role:str) -> None:
    # Initialization
    access_allowed=("admin", "purchaser") # Only admin and purchaser can acceess
    data_list = []

    print("You are now at ▶ View Replenish List ◀\n")
    print("Please replenish items below:\n")
    
    # Check user's role
    if role not in access_allowed:
        print("REJECTED: You have no permission to access this, please login again!")
    else:
        # Get items 2D List
        data_list=inventory_data_list()

        # Display items with quantity lower than minimum
        print("{:10} {:20} {:15} {:10} {:10} {:10} {:10}".format(*["Code", "Description", "Category", "Unit", "Price", "Quantity", "Minimum (Threshold)"]))
        for row in data_list:
            if int(row[5])<int(row[6]):
                print("{:10} {:20} {:15} {:10} {:10}\t{:10}\t{:10}".format(*row))

        # Return to main menu after user finish reading
        input("Type any character to exit after finish reading: ")
    print("Exit view replenish list")

def search_items(role:str) -> None:
    # Assume that "inventory.txt" is placed in the same directory as this file

    #Initialize
    access_allowed=("admin","inventory-checker", "purchaser") # Only admin and inventory checker can search items
    data_ls=[]

    #Welcome message
    print("\nYou are now at: ▶ Search Items ◀\n")
    
    # Validate user type
    while True: 
        if role not in access_allowed:
            print("REJECTED: You have no permission to access this, please login again!")
            break 
        try:
            # Get items 2D List
            data_ls=inventory_data_list()
 
            print("\nTo search items, please choose which method you want to use to search your required items \n 1.Description \n 2.Code range \n 3.Category \n 4.Price ")
            print("Type 'q' to go back to main menu.")

            # Let user to choose a method
            Method=input("\nPlease enter the method number: ")

            if Method.strip()=="q": # User requests to exit
                break #returns to main menu
            elif Method.isdecimal() and 0<int(Method)<=4: # If user enter a valid option
                found=False
                if Method.strip()=="1": # Search using description
                    Description = input("Please input the item's description: ").strip()

                    # Display item list
                    print("{:10} {:20} {:15} {:10} {:10} {:10} {:10}".format(*["Code", "Description", "Category", "Unit", "Price", "Quantity", "Minimum (Threshold)"]))
                    for row in range(len(data_ls)): 
                        if data_ls[row][1].strip().lower()==Description.lower():
                            print("{:10} {:20} {:15} {:10} {:10}\t{:10}\t{:10}".format(*data_ls[row]))
                            found=True
                        if row==(len(data_ls)-1) and found: # Search until the end of file
                            break
                    else: # If no item is displayed
                        raise Exception("Item cannot be found")

                elif Method.strip()=="2": # Search using item code range
                    print("Enter item code range separated by '~'")
                    print("Format: <initial>~<final>")
                    print("Example: 30000~39999")
                    CodeRange=input("Please enter item code range based on format: ").strip().split("~")
                    if len(CodeRange)!=2: # If wrong input format
                        raise Exception("Please enter input based on format!")
                    
                    # If item code is in invalid format
                    elif not CodeRange[0].isdecimal() or not CodeRange[1].isdecimal() or len(CodeRange[0])!=5 or len(CodeRange[1])!=5:
                        raise Exception("Please enter 5-digit item code for both initial and final!")
                        
                    elif int(CodeRange[0])>int(CodeRange[1]): # If initial smaller than final
                        raise Exception("Initial must be smaller than final!")
                    
                    # Display item list
                    print("{:10} {:20} {:15} {:10} {:10} {:10} {:10}".format(*["Code", "Description", "Category", "Unit", "Price", "Quantity", "Minimum (Threshold)"]))
                    for row in range(len(data_ls)):
                        if int(data_ls[row][0]) in range(int(CodeRange[0]), int(CodeRange[1])+1):
                            print("{:10} {:20} {:15} {:10} {:10}\t{:10}\t{:10}".format(*data_ls[row]))
                            found=True
                        if row==(len(data_ls)-1) and found: # Search until the end of file
                            break
                    else:
                        raise Exception("Item cannot be found")

                elif Method.strip()=="3": # Search using item category
                    Category = input("Please input the item category: ").strip()

                    # Display item list
                    print("{:10} {:20} {:15} {:10} {:10} {:10} {:10}".format(*["Code", "Description", "Category", "Unit", "Price", "Quantity", "Minimum (Threshold)"]))
                    for row in range(len(data_ls)):
                        if data_ls[row][2].strip().lower()==Category.lower():
                            print("{:10} {:20} {:15} {:10} {:10}\t{:10}\t{:10}".format(*data_ls[row]))
                            found=True
                        if row==(len(data_ls)-1) and found: # Search until the end of file
                            break
                    else:
                        raise Exception("Item cannot be found")

                elif Method.strip()=="4": # Search using price range
                    print("Enter the item price range\nWARNING: All prices will be rounded to 2 decimal")
                    try:
                        min="%.2f" % (float(input("Price min: "))) # Convert to 2 decimal
                        max="%.2f" % (float(input("Price max: "))) # Convert to 2 decimal
                    except ValueError: # If entered values are not number
                        raise Exception("Price must be number!")
                    
                    # Display item list
                    print("{:10} {:20} {:15} {:10} {:10} {:10} {:10}".format(*["Code", "Description", "Category", "Unit", "Price", "Quantity", "Minimum (Threshold)"]))
                    for row in range(len(data_ls)):
                        if float(min) <= float(data_ls[row][4]) <= float(max):
                            print("{:10} {:20} {:15} {:10} {:10}\t{:10}\t{:10}".format(*data_ls[row]))
                            found=True
                        if row==(len(data_ls)-1) and found:
                            break
                    else:
                        raise Exception("Item cannot be found")
            else:
                raise Exception("Invalid option!")
        except Exception as e:
            print("\nERROR:",e)

    print("EXIT search item")

# This system will not run automatically if it's imported as module in another file
if __name__=='__main__':
    main()