NoneType error when converting tuple to list

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

Straight from the docs "Fetches the next row of a query result set, returning a single sequence, or None when no more data is available" — Bhargav Rao
– Bhargav Rao, Commented Apr 2, 2015 at 9:51

Martijn Pieters · Accepted Answer · 2015-04-02 09:50:00Z

4

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 [])

answered Apr 2, 2015 at 9:50

Martijn Pieters

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