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A generally useful event scheduler class. Each instance of this class manages its own queue. No multi-threading is implied; you are supposed to hack that yourself, or use a single instance per application. Each instance is parametrized with two functions, one that is supposed to return the current time, one that is supposed to implement a delay. You can implement real-time scheduling by substituting time and sleep from built-in module time, or you can implement simulated time by writing your own functions. This can also be used to integrate scheduling with STDWIN events; the delay function is allowed to modify the queue. Time can be expressed as integers or floating point numbers, as long as it is consistent. Events are specified by tuples (time, priority, action, argument, kwargs). As in UNIX, lower priority numbers mean higher priority; in this way the queue can be maintained as a priority queue. Execution of the event means calling the action function, passing it the argument sequence in "argument" (remember that in Python, multiple function arguments are be packed in a sequence) and keyword parameters in "kwargs". The action function may be an instance method so it has another way to reference private data (besides global variables).
Event(time, priority, sequence, action, argument, kwargs)
count(self, value, /) Return number of occurrences of value.
index(self, value, start=0, stop=9223372036854775807, /) Return first index of value. Raises ValueError if the value is not present.
action = _tuplegetter(3, 'Executing the event means executing\naction(*argument, **kwargs)') Executing the event means executing action(*argument, **kwargs)
argument = _tuplegetter(4, 'argument is a sequence holding the positional\narguments for the action.') argument is a sequence holding the positional arguments for the action.
kwargs = _tuplegetter(5, 'kwargs is a dictionary holding the keyword\narguments for the action.') kwargs is a dictionary holding the keyword arguments for the action.
priority = _tuplegetter(1, 'Events scheduled for the same time will be executed\nin the order of their priority.') Events scheduled for the same time will be executed in the order of their priority.
sequence = _tuplegetter(2, 'A continually increasing sequence number that\n separates events if time and priority are equal.')
A continually increasing sequence number that
separates events if time and priority are equal.
time = _tuplegetter(0, 'Numeric type compatible with the return value of the\ntimefunc function passed to the constructor.') Numeric type compatible with the return value of the timefunc function passed to the constructor.
Return a count object whose .__next__() method returns consecutive values.
Equivalent to:
def count(firstval=0, step=1):
x = firstval
while 1:
yield x
x += step
cancel(self, event)
Remove an event from the queue.
This must be presented the ID as returned by enter().
If the event is not in the queue, this raises ValueError.
empty(self) Check whether the queue is empty.
enter(self, delay, priority, action, argument=(), kwargs=<object object at 0x7f75e3c96490>)
A variant that specifies the time as a relative time.
This is actually the more commonly used interface.
enterabs(self, time, priority, action, argument=(), kwargs=<object object at 0x7f75e3c96490>)
Enter a new event in the queue at an absolute time.
Returns an ID for the event which can be used to remove it,
if necessary.
run(self, blocking=True)
Execute events until the queue is empty.
If blocking is False executes the scheduled events due to
expire soonest (if any) and then return the deadline of the
next scheduled call in the scheduler.
When there is a positive delay until the first event, the
delay function is called and the event is left in the queue;
otherwise, the event is removed from the queue and executed
(its action function is called, passing it the argument). If
the delay function returns prematurely, it is simply
restarted.
It is legal for both the delay function and the action
function to modify the queue or to raise an exception;
exceptions are not caught but the scheduler's state remains
well-defined so run() may be called again.
A questionable hack is added to allow other threads to run:
just after an event is executed, a delay of 0 is executed, to
avoid monopolizing the CPU when other threads are also
runnable.
queue = <property object at 0x7f75e0be8130>
An ordered list of upcoming events.
Events are named tuples with fields for:
time, priority, action, arguments, kwargs
namedtuple(typename, field_names, *, rename=False, defaults=None, module=None)
Returns a new subclass of tuple with named fields.
>>> Point = namedtuple('Point', ['x', 'y'])
>>> Point.__doc__ # docstring for the new class
'Point(x, y)'
>>> p = Point(11, y=22) # instantiate with positional args or keywords
>>> p[0] + p[1] # indexable like a plain tuple
33
>>> x, y = p # unpack like a regular tuple
>>> x, y
(11, 22)
>>> p.x + p.y # fields also accessible by name
33
>>> d = p._asdict() # convert to a dictionary
>>> d['x']
11
>>> Point(**d) # convert from a dictionary
Point(x=11, y=22)
>>> p._replace(x=100) # _replace() is like str.replace() but targets named fields
Point(x=100, y=22)