human
Here's a good function header given the following:
I wrote the below code

    msg = MIMEText(message)
    msg['Subject'] = subject
    msg['From'] = sender
    msg['To'] = ',    '.join(recipients)
    dfr = sendmail(host, sender, recipients, msg.as_string())
    def success(r):
        reactor.stop()
    def error(e):
        print(e)
        reactor.stop()
    dfr.addCallback(success)
    dfr.addErrback(error)
    reactor.run()

What's a good function header?
assistant
#Here's a good function header.

def send(message, subject, sender, recipients, host):