Hi all,

is there a feature or pattern for adding a listener that is to be executed 
(at most) once? For example, say you want to send an email when user is 
created and the session is committed. If event.listen() supported a "once" 
boolean parameter, this could be expressed as:

def email_user(email_address, message):
   ...
...
if  valid_data:
    new_user = User(**valid_data)
    db.session.add(new_user)
    # send an email to new_user after committing
    event.listen(db.session, "after_commit", 
                       once=True, # hypothetical parameter
                       lambda session: email_user(new_user.email, "welcome 
{}!".format(new_user.name))

Thanks,
George

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