Skip None values in entry widgets Tkinter Python

Let’s say we have a Tkinter app with many entry widgets like this:

root = Tk()

entry1 = Entry(root, width=40)
entry1.grid(row=0, column=0)
entry2 = Entry(root, width=40)
enrtry2.grid(row=1,column=0)
entry3 = Entry(root, width=40)
enrtry3.grid(row=2,column=0)
entry4 = Entry(root, width=40)
enrtry4.grid(row=3,column=0)

root.mainloop()

The values from these widgets are used to UPDATE a database. The thing I want is to be able to skip a value in anyone of them and not use it in the UPDATE statement. For now with my code I check if there is something written in the widgets like this:

db = fdb.connector
c = db.cursor

values = [entry1.get(), entry2.get(), entry3.get(), entry4.get()]

for v in values:
   if len(v) == 0 or v is None:
     pass
   elif lev(v) != 0:
     c.execute(f"""UPDATE table1 SET column1 = {v[0]}, column2 = {v[1]}, column3 = {v[2]}, column4 = {v[3]} WHERE ID = 1;""")

The problem is that when one of the values is None in the database I get a value of NULL which is correct, because there is no value in the widget. How can I ‘tell’ python that when there is no value presented it should skip that value and continue to update just the others?

EDIT: Thanks to @TheLizzard this solution works like a charm:

string = "UPDATE table1 SET "
        at_least_one_set = False
        for i in range(12):
             if v[i] != "":
                 string += columns[i] + " = " + "'" + str(v[i]) + "'" + ", "
                 at_least_one_set = True
        if at_least_one_set:
            string = string[:-2]
            string += f" WHERE column_a = '{v[0]}' OR column_b = '{v[1]}';"
            c.execute(string)
        else:
            print("No values were set. Raise an error?")

EDIT2: After a bit of research, and thanks to @TheLizzard, @Arioch ‘The, @Mark Rotteveel I’ve come with the following working code and following one of the suggestions here this is safe now:

v = ["", "2", "3", ""]
column_names = ["column_a", "column_b", "column_c", "column_z"]
rowids = [row[0] for row in c.execute("SELECT id FROM table1 WHERE column_a = ? OR column_b = ?", (v[0], v[1], ))]

string = "UPDATE table1 SET "
at_least_one_set = False
for i in range(12):
    if v[i] != "":
        string += columns[i] + " = '{}'".format(v[i]) + ", "
        at_least_one_set = True
if at_least_one_set:
   string = string[:-2]
   string += " WHERE id = {}".format(rowids[0]) + ";"
   c.execute(string)

And the result is:

UPDATE table1 SET column_b = '2', column_c = '3' WHERE id = 1;

Answer

Try this:

v = ["", "2", "3", ""]
column_names = ["column_a", "column_b", "column_c", "column_z"]


string = "UPDATE table1 SET "
at_least_one_set = False
for i in range(4):
    if v[i] != "":
        string += column_names[i] + " = " + v[i] + ", "
        at_least_one_set = True
if at_least_one_set:
    string = string[:-2]
    string += ";"
    print(string)
else:
    print("No values were set. Raise an error?")

I dynamically create a string starting with "UPDATE table1 SET " and ending in ";" where I skip all of the values that are "".