python中的变量更改回调 [英] Callback on variable change in python
问题描述
我已经搜索了周围,但没有找到类似的东西。假设我有很多线程,它们不断读取和更新整数变量 x
。我希望在 x
改变一定幅度(例如500)时运行回调。
I've searched around but didn't find anything like this. Let's say I have an army of threads, that keep reading and updating an integer variable x
. I would like a callback for when x
changes over a certain margin, let's say 500, to run the callback.
如何在不增加系统负担的情况下完成此操作,例如使线程具有而为真
并检查变量是否已更改?性能至关重要。伦理学也是如此。
How can this be done without putting a heavy load on the system, like having a thread that has a while true
and checks if the variable has changed? Performance is critical. But so are ethics.
用普通代码是这样的:
x = 10
def runMe():
print('Its greater than 500!!')
def whenToRun():
return x >= 500
triggers.event(runMe, whenToRun)
推荐答案
您想要一个函数(一个 setter ),该函数在变量的值更改时被调用。做到这一点的一种好方法是定义 @property
。它的行为类似于变量,但具有 getter 函数和 setter 函数。
You want to have a function (a "setter") which is called whenever the variable's value changes. A good way to do that is to define a @property
. It will behave like a variable, but will have a getter function and a setter function.
然后,在设置器,调用所需的任何回调,这些回调将对更改做出反应。
Then, in the setter, call any callbacks you need, which will react to the change.
这应该可以解决问题:
class ObjectHoldingTheValue:
def __init__(self, initial_value=0):
self._value = initial_value
self._callbacks = []
@property
def value(self):
return self._value
@value.setter
def value(self, new_value):
old_value = self._value
self._value = new_value
self._notify_observers(old_value, new_value)
def _notify_observers(self, old_value, new_value):
for callback in self._callbacks:
callback(old_value, new_value)
def register_callback(self, callback):
self._callbacks.append(callback)
然后,您可以执行以下操作:
Then, you can do:
def print_if_change_greater_than_500(old_value, new_value):
if abs(old_value - new_value) > 500:
print(f'The value changed by more than 500 (from {old_value} to {new_value})')
holder = ObjectHoldingTheValue()
holder.register_callback(print_if_change_greater_than_500)
holder.value = 7 # nothing is printed
holder.value = 70 # nothing is printed
holder.value = 700 # a message is printed
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