Python sqlite3 OperationalError: near "?": syntax error - python-2.7

Question

Trying to let users update column values on existing records for a specific table named "Scenario." The record being updated is identified by an index column called "Scenario_Key", unique to each instance of this class. The code I already have produces a dictionary of key, value pairs where key is the name of the column being updated and value is the value being inserted into it. To update the sqlite database I'm trying the following:
cursor.execute("""UPDATE Scenario SET ?=? WHERE Scenario_Key=?;""", (key, new_val, self.scenario_key))
But when I try to execute by clicking the "Save and Close" button, I get the following:
Traceback (most recent call last):
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk/Tkinter.py", line 1536, in __call__
return self.func(*args)
File "/Users/xxx/Documents/Consulting/DCA/Damage Control Assistant/EditScenarioWindow.py", line 91, in <lambda>
SaveAndCloseButton = Button(ButtonFrame, text="Save and Close", command=lambda: self.SaveAndCloseWindow())
File "/Users/xxx/Documents/Consulting/DCA/Damage Control Assistant/EditScenarioWindow.py", line 119, in SaveAndCloseWindow
cursor.execute(cmd_string, (key, new_val, self.scenario_key))
OperationalError: near "?": syntax error
I've read over sqlite3.OperationalError: near "?": syntax error, but I'm trying to do a single sqlite query where all the variables have already been calculated, not get values from the database and build a query from there. I'm supplying the positional arguments as a tuple. So why doesn't sqlite3 like the query I'm submitting?

Answer 1

You cannot parametrize column names. While being cognisant of the possibility of SQL Injection attacks, you could instead do:
cursor.execute("""UPDATE Scenario
SET {}=?
WHERE Scenario_Key=?;""".format(key),
(new_val, self.scenario_key))