mirror of
https://github.com/KevinMidboe/python-gpiozero.git
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The source/values toolkit
Me and my big mouth. No sooner do I declare the base classes "relatively stable" than I go and mess around with it all again. Anyway, this is the long promised set of utilities to make source/values more interesting. It includes a few interesting little utility functions, a whole bunch of examples and introduces the notion of "pseudo" devices with no (obvious) hardware representation like a time-of-day device. This necessitated making the event system a little more generic (it's not exclusive the GPIO devices after all; no reason we can't use it on composite devices in future) and by this point the mixins have gotten large enough to justify their own module. The pseudo-devices are a bit spartan and basic at the moment but I'm sure there'll be plenty of future ideas...
This commit is contained in:
Dave Jones
326
gpiozero/mixins.py
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326
gpiozero/mixins.py
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from __future__ import (
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unicode_literals,
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print_function,
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absolute_import,
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division,
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)
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nstr = str
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str = type('')
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import inspect
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import weakref
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from functools import wraps
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from threading import Event
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from collections import deque
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try:
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from statistics import median, mean
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except ImportError:
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from .compat import median, mean
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from .threads import GPIOThread
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from .exc import BadEventHandler, DeviceClosed
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class ValuesMixin(object):
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"""
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Adds a :attr:`values` property to the class which returns an infinite
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generator of readings from the :attr:`value` property.
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.. note::
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Use this mixin *first* in the parent class list.
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"""
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@property
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def values(self):
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"""
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An infinite iterator of values read from `value`.
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"""
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while True:
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try:
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yield self.value
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except DeviceClosed:
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break
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class SourceMixin(object):
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"""
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Adds a :attr:`source` property to the class which, given an iterable,
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sets :attr:`value` to each member of that iterable until it is exhausted.
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.. note::
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Use this mixin *first* in the parent class list.
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"""
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def __init__(self, *args, **kwargs):
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self._source = None
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self._source_thread = None
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self._source_delay = 0.01
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super(SourceMixin, self).__init__(*args, **kwargs)
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def close(self):
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try:
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super(SourceMixin, self).close()
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except AttributeError:
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pass
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self.source = None
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def _copy_values(self, source):
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for v in source:
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self.value = v
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if self._source_thread.stopping.wait(self._source_delay):
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break
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@property
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def source_delay(self):
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"""
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The delay (measured in seconds) in the loop used to read values from
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:attr:`source`. Defaults to 0.01 seconds which is generally sufficient
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to keep CPU usage to a minimum while providing adequate responsiveness.
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"""
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return self._source_delay
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@source_delay.setter
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def source_delay(self, value):
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if value < 0:
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raise GPIOBadSourceDelay('source_delay must be 0 or greater')
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self._source_delay = float(value)
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@property
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def source(self):
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"""
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The iterable to use as a source of values for :attr:`value`.
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"""
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return self._source
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@source.setter
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def source(self, value):
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if self._source_thread is not None:
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self._source_thread.stop()
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self._source_thread = None
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self._source = value
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if value is not None:
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self._source_thread = GPIOThread(target=self._copy_values, args=(value,))
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self._source_thread.start()
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class SharedMixin(object):
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"""
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This mixin marks a class as "shared". In this case, the meta-class
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(GPIOMeta) will use :meth:`_shared_key` to convert the constructor
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arguments to an immutable key, and will check whether any existing
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instances match that key. If they do, they will be returned by the
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constructor instead of a new instance. An internal reference counter is
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used to determine how many times an instance has been "constructed" in this
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way.
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When :meth:`close` is called, an internal reference counter will be
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decremented and the instance will only close when it reaches zero.
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"""
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_INSTANCES = {}
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def __del__(self):
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self._refs = 0
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super(SharedMixin, self).__del__()
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@classmethod
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def _shared_key(cls, *args, **kwargs):
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"""
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Given the constructor arguments, returns an immutable key representing
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the instance. The default simply assumes all positional arguments are
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immutable.
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"""
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return args
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class EventsMixin(object):
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"""
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Adds edge-detected :meth:`when_activated` and :meth:`when_deactivated`
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events to a device based on changes to the :attr:`~Device.is_active`
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property common to all devices. Also adds :meth:`wait_for_active` and
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:meth:`wait_for_inactive` methods for level-waiting.
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.. note::
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Note that this mixin provides no means of actually firing its events;
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call :meth:`_fire_events` in sub-classes when device state changes to
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trigger the events. This should also be called once at the end of
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initialization to set initial states.
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"""
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def __init__(self, *args, **kwargs):
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super(EventsMixin, self).__init__(*args, **kwargs)
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self._active_event = Event()
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self._inactive_event = Event()
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self._when_activated = None
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self._when_deactivated = None
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self._last_state = None
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def wait_for_active(self, timeout=None):
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"""
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Pause the script until the device is activated, or the timeout is
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reached.
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:param float timeout:
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Number of seconds to wait before proceeding. If this is ``None``
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(the default), then wait indefinitely until the device is active.
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"""
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return self._active_event.wait(timeout)
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def wait_for_inactive(self, timeout=None):
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"""
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Pause the script until the device is deactivated, or the timeout is
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reached.
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:param float timeout:
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Number of seconds to wait before proceeding. If this is ``None``
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(the default), then wait indefinitely until the device is inactive.
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"""
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return self._inactive_event.wait(timeout)
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@property
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def when_activated(self):
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"""
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The function to run when the device changes state from inactive to
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active.
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This can be set to a function which accepts no (mandatory) parameters,
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or a Python function which accepts a single mandatory parameter (with
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as many optional parameters as you like). If the function accepts a
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single mandatory parameter, the device that activated will be passed
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as that parameter.
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Set this property to ``None`` (the default) to disable the event.
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"""
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return self._when_activated
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@when_activated.setter
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def when_activated(self, value):
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self._when_activated = self._wrap_callback(value)
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@property
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def when_deactivated(self):
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"""
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The function to run when the device changes state from active to
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inactive.
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This can be set to a function which accepts no (mandatory) parameters,
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or a Python function which accepts a single mandatory parameter (with
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as many optional parameters as you like). If the function accepts a
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single mandatory parameter, the device that deactivated will be
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passed as that parameter.
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Set this property to ``None`` (the default) to disable the event.
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"""
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return self._when_deactivated
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@when_deactivated.setter
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def when_deactivated(self, value):
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self._when_deactivated = self._wrap_callback(value)
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def _wrap_callback(self, fn):
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if fn is None:
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return None
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elif not callable(fn):
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raise BadEventHandler('value must be None or a callable')
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elif inspect.isbuiltin(fn):
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# We can't introspect the prototype of builtins. In this case we
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# assume that the builtin has no (mandatory) parameters; this is
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# the most reasonable assumption on the basis that pre-existing
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# builtins have no knowledge of gpiozero, and the sole parameter
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# we would pass is a gpiozero object
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return fn
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else:
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# Try binding ourselves to the argspec of the provided callable.
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# If this works, assume the function is capable of accepting no
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# parameters
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try:
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inspect.getcallargs(fn)
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return fn
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except TypeError:
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try:
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# If the above fails, try binding with a single parameter
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# (ourselves). If this works, wrap the specified callback
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inspect.getcallargs(fn, self)
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@wraps(fn)
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def wrapper():
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return fn(self)
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return wrapper
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except TypeError:
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raise BadEventHandler(
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'value must be a callable which accepts up to one '
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'mandatory parameter')
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def _fire_events(self):
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old_state = self._last_state
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new_state = self._last_state = self.is_active
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if old_state is None:
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# Initial "indeterminate" state; set events but don't fire
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# callbacks as there's not necessarily an edge
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if new_state:
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self._active_event.set()
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else:
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self._inactive_event.set()
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else:
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if not old_state and new_state:
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self._inactive_event.clear()
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self._active_event.set()
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if self.when_activated:
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self.when_activated()
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elif old_state and not new_state:
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self._active_event.clear()
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self._inactive_event.set()
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if self.when_deactivated:
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self.when_deactivated()
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class GPIOQueue(GPIOThread):
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"""
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Extends :class:`GPIOThread`. Provides a background thread that monitors a
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device's values and provides a running *average* (defaults to median) of
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those values. If the *parent* device includes the :class:`EventsMixin` in
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its ancestry, the thread automatically calls
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:meth:`~EventsMixin._fire_events`.
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"""
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def __init__(
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self, parent, queue_len=5, sample_wait=0.0, partial=False,
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average=median):
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assert callable(average)
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super(GPIOQueue, self).__init__(target=self.fill)
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if queue_len < 1:
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raise GPIOBadQueueLen('queue_len must be at least one')
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if sample_wait < 0:
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raise GPIOBadSampleWait('sample_wait must be 0 or greater')
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self.queue = deque(maxlen=queue_len)
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self.partial = partial
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self.sample_wait = sample_wait
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self.full = Event()
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self.parent = weakref.proxy(parent)
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self.average = average
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@property
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def value(self):
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if not self.partial:
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self.full.wait()
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try:
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return self.average(self.queue)
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except ZeroDivisionError:
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# No data == inactive value
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return 0.0
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def fill(self):
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try:
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while (not self.stopping.wait(self.sample_wait) and
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len(self.queue) < self.queue.maxlen):
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self.queue.append(self.parent._read())
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if self.partial and isinstance(self.parent, EventsMixin):
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self.parent._fire_events()
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self.full.set()
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while not self.stopping.wait(self.sample_wait):
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self.queue.append(self.parent._read())
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if isinstance(self.parent, EventsMixin):
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self.parent._fire_events()
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except ReferenceError:
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# Parent is dead; time to die!
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pass
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