import re


def _extract_command(text):
    """
    >>> _extract_command('/start')
    ('start', None)
    >>> _extract_command('/send_at 12:00 3')
    ('send_at', '12:00 3')
    """
    m = re.match(r'^/([^ ]+)( (.+))?', text)
    if not m:
        raise Exception("Cannot parse command %r" % text)
    return m.group(1), m.group(3)