将元组转换为列表时，NoneType错误

Question

I am trying to select a row from a sqlite database. Make a number of changes then commit them back to the sqlite database as well as a mysql database.

The way I am trying to do it is by converting the tuple retrieved by the SELECT query into a list to make the changes.

key = 27361
c.execute("SELECT * FROM employees WHERE key = ?", (key,))
employeeTuple = c.fetchone()
employeeList = list(employeeTuple)

I am getting an error:

TypeError: 'NoneType' object is not iterable

Answer 1

cursor.fetchone() returns None if there are no matching rows. You have no rows where key = 27361 matches.

You can test for that possibility using if employeeTuple or using or to shortcircuit and assign None to employeeList in that case:

# if employeeTuple is None employeeList will not be set at all
if employeeTuple:
    employeeList = list(employeeTuple)

or

# if employeeTuple is None employeeList will be set to None
employeeList = employeeTuple or list(employeeTuple)

or

# if employeeTuple is None employeeList will be set to the empty list
employeeList = list(employeeTuple or [])