concatenate strings with atomic update in peewee using sqlite db

I would like to update a text field in an sqlite database created using the peewee python library. Specifically I would like to use peewee's atomic updates something like:

query = Table.update(textfield = Table.textfield + 'string').where(some condition)

query.execute()

This type of update works fine for numeric fields but not for text fields. I'm guessing there may be a way to do this with the sqlite || operator, but as sql in general is somewhat new to me I am unable to figure it out.