Help with python 'not subscriptable' error

[Extra]

Hello,

I have this chunk of code from my PyQt GUI that gets a result from a SQLite table and uses that result to do a math calculation.

Snippet:

else: 
                        #Connect to the inventory database (inventory.db)
                        connection = sqlite3.connect(InventoryDatabase)
                        cursor = connection.cursor()
                        cursor.execute("SELECT Sell_Price_$ FROM items WHERE Name = ?",(SelectedItemName,))
                        connection.commit()
                        SellPrice = cursor.fetchone()
                        
                        # #Update the quantity
                        # cursor.execute("UPDATE items SET Quantity = Quantity - ? WHERE Name = ?",(SelectedItemQuantity, SelectedItemName,))
                        # connection.commit()
                        
                        #Close the connection
                        connection.close()

                        print('Selcted Item Quantity: ', SelectedItemQuantity)

                        x = float(SelectedItemQuantity)
                        print('Float Value = ', x)
                        y = SellPrice[0]
                        print("y = ",y)
                        z = float(y)
                        print('x*z= ', x*z)
                        MaterialUsedPrice2 = x*z

                        #Calculate the Price of Material Used
                        #MaterialUsedPrice = SelectedItemQuantity * SellPrice
                        print('The Total Price for the', '(',x,')', SelectedItemName, ' Used is: $', MaterialUsedPrice2)

Output:

Output:
2 , 1/2" PVC Coupling
('PVC',)
Selcted Item Quantity:  2
Float Value =  2.0
y =  1.5
x*z=  3.0
The Total Price for the ( 2.0 ) 1/2" PVC Coupling  Used is: $ 3.0

#I don't know why this gets printed (again...Since it's already been printed above (Selcted Item Quantity:  2
Float Value =  2.0) and I don't know why the values are 0)
0 , -
None
Selcted Item Quantity:  0
Float Value =  0.0

y = SellPrice[0]
TypeError: 'NoneType' object is not subscriptable

I get this error and I don't know why (When I do print("y = ",y) I get 1.5, which is the correct value, so why am I getting this error?)

Error:
y = SellPrice[0]
TypeError: 'NoneType' object is not subscriptable

Why do I get this error and how do I fix it?

Thanks in advance.

Full function (If it helps):

    def SubmitClicked(self):
        #Get User Inputted Quantity & Material
        #Probably going to have to do it the long way: Do all 22 comboBoxes individually. 
        for widget in self.MaterialUsedFrame.children():        
            if isinstance(widget, QSpinBox):
                    SelectedItemQuantity = widget.text()
            if isinstance(widget,QComboBox):
                    SelectedItemName = widget.currentText()
                    print(SelectedItemQuantity, ',' ,SelectedItemName)
        
                    #Connect to the inventory database (inventory.db)
                    connection = sqlite3.connect(InventoryDatabase)
                    cursor = connection.cursor()
                    cursor.execute("SELECT Main_Category FROM items WHERE Name = ?",(SelectedItemName,))
                    connection.commit()
                    Result = cursor.fetchone()
                    #Close the connection
                    connection.close()
                    print(Result)

                    if Result == ('Wire',):
                        #Connect to the inventory database (inventory.db)
                        connection = sqlite3.connect(InventoryDatabase)
                        cursor = connection.cursor()
                        cursor.execute("SELECT Price_Per_Ft FROM items WHERE Name = ?",(SelectedItemName,))
                        connection.commit()
                        PricePerFt = cursor.fetchone()
                        #Close the connection
                        connection.close()
                        print(PricePerFt)
                        
                        #Might be better off making all those SpinBoxes Labels
                        #& Just setting the text to the price
                        for widget in self.MaterialPriceFrame.children():        
                            if isinstance(widget, QDoubleSpinBox):
                                widget.setValue(80.80)

                    else: 
                        #Connect to the inventory database (inventory.db)
                        connection = sqlite3.connect(InventoryDatabase)
                        cursor = connection.cursor()
                        cursor.execute("SELECT Sell_Price_$ FROM items WHERE Name = ?",(SelectedItemName,))
                        connection.commit()
                        SellPrice = cursor.fetchone()
                        
                        # #Update the quantity
                        # cursor.execute("UPDATE items SET Quantity = Quantity - ? WHERE Name = ?",(SelectedItemQuantity, SelectedItemName,))
                        # connection.commit()
                        
                        #Close the connection
                        connection.close()

                        print('Selcted Item Quantity: ', SelectedItemQuantity)

                        x = float(SelectedItemQuantity)
                        print('Float Value = ', x)
                        y = SellPrice[0]
                        print("y = ",y)
                        z = float(y)
                        print('x*z= ', x*z)
                        MaterialUsedPrice2 = x*z

                        #Calculate the Price of Material Used
                        #MaterialUsedPrice = SelectedItemQuantity * SellPrice
                        print('The Total Price for the', '(',x,')', SelectedItemName, ' Used is: $', MaterialUsedPrice2)
#----------------------------------------------------------------------------------------------------

[ndc85430]

The error is because SellPrice has the value None. You need to work out why that is - looks like no value was returned from your database query.

[deanhystad]

fetchone()
If row_factory is None, return the next row query result set as a tuple. Else, pass it to the row factory and return its result. Return None if no more data is available.

row_factor is None because NO MORE DATA IS AVAILABLE. Maybe there never was any data to start with, or maybe you already retrieved all the data. I'm guessing the former looking at your code. It doesn't matter the reason why, what matters is that the documentation for fetch_one() says that it might return None, and your program does nothing to prevent that highly likely possibility from crashing the program.

[woooee]

I have always used double equal signs

WHERE Name == ?