Timers 有一下选项可以用于控制相关操作：

• Timer based in absolute time input or with regards to session start/end times

• Timezone specification for the time specification, be it directly or via pytz compatible objects or via data feed session end times

• Starting offset with regards to the specified time

• Repetitions intervals

• Weekdays filter (with carry over option)

• Monthdays filter (with carry over option)

-Custom callback filter

Usage pasttern

Both in Cerebro and Strategy subclasses the timer callback will be received in the following method.

def notify_timer(self, timer, when, *args, **kwargs):
    '''Receives a timer notification where ``timer`` is the timer which was
    returned by ``add_timer``, and ``when`` is the calling time. ``args``
    and ``kwargs`` are any additional arguments passed to ``add_timer``

    The actual ``when`` time can be later, but the system may have not be
    able to call the timer before. This value is the timer value and not the
    system time.
    '''

• Adding timers - Via Strategy
• Adding timers - Via Cerebro

Done with the same method and just the addition of the parameter strats. If set to True the timer will not only be notified to the cerebro, it will also be notified to all strategies running in the system. strats 设定为True 则Timer作用于这个回测系统，不只是cerebro

def add_timer(self, when,
              offset=datetime.timedelta(), repeat=datetime.timedelta(),
              weekdays=[], weekcarry=False,
              monthdays=[], monthcarry=True,
              allow=None,
              tzdata=None, cheat=False, strats=False,
              *args, **kwargs):
    '''

Parameters to add_timer

• when: can be

• datetime.time instance (see below tzdata)

• bt.timer.SESSION_START to reference a session start

• bt.timer.SESSION_END to reference a session end

• offset which must be a datetime.timedelta instance

Used to offset the value when. It has a meaningful use in combination with SESSION_START and SESSION_END, to indicated things like a timer being called 15 minutes after the session start.

• repeat which must be a datetime.timedelta instance
  Indicates if after a 1st call, further calls will be scheduled within the same session at the scheduled repeat delta

Once the timer goes over the end of the session it is reset to the original value for when

• weekdays: a sorted iterable with integers indicating on which days (iso codes, Monday is 1, Sunday is 7) the timers can be actually invoked
  If not specified, the timer will be active on all days

• weekcarry (default: False). If True and the weekday was not seen (ex: trading holiday), the timer will be executed on the next day (even if in a new week)

• monthdays: a sorted iterable with integers indicating on which days of the month a timer has to be executed. For example always on day 15 of the month

If not specified, the timer will be active on all days

• monthcarry (default: True). If the day was not seen (weekend, trading holiday), the timer will be executed on the next available day.

• allow (default: None). A callback which receives a datetime.date` instance and returns True if the date is allowed for timers or else returns False

• tzdata which can be either None (default), a pytz instance or a data feed instance.

None: when is interpreted at face value (which translates to handling it as if it where UTC even if it’s not)

• pytz instance: when will be interpreted as being specified in the local time specified by the timezone instance.

• data feed instance: when will be interpreted as being specified in the local time specified by the tz parameter of the data feed instance.
  [Note] If when is either SESSION_START or SESSION_END and tzdata is
  None, the 1st data feed in the system (aka self.data0) will be
  used as the reference to find out the session times.

• strats (default: False) call also the notify_timer of strategies

• cheat (default False) if True the timer will be called before the broker has a chance to evaluate the orders. This opens the chance to issue orders based on opening price for example right before the session starts

• *args: any extra args will be passed to notify_timer

• **kwargs: any extra kwargs will be passed to notify_timer

Example for allow=callable

allow=callable where the callable accepts datetime.date instance. Notice this is not a datetime.datetime instance, because the allow callable is only meant to decide if a given day is suitable for timers or not.

To implement something like the rule laid out above:

class FutOpExp(object):
    def __init__(self):
        self.fridays = 0
        self.curmonth = -1

    def __call__(self, d):
        _, _, isowkday = d.isocalendar()

        if d.month != self.curmonth:
            self.curmonth = d.month
            self.fridays = 0

        # Mon=1 ... Sun=7
        if isowkday == 5 and   self.curmonth in [3, 6, 9, 12]:
            self.fridays += 1

            if self.friday == 3:  # 3rd Friday
                return True  # timer allowed

        return False  # timer disallowed

And one would pass allow=FutOpeExp() to the creation of the timer

This would allow a timer to kick in on the 3rd Friday of those months and may be close positions before the futures expire.