Python One-Shot，水平触发，边缘触发

Question

我正在监控 python-twisted 框架中的 bool 值。当 bool 值改变时，我只想执行一次函数。这可以用 Python 完成吗？

我正在从 IO 设备中串行提取 bool 值。在某个时间间隔轮询该值。当值改变时我想执行一个函数。

Answer 1

用类比用全局变量更好。

class EdgeTrigger(object):
    def __init__(self, callback):
        self.value = None
        self.callback = callback

    def __call__(self, value):
        if value != self.value:
            self.callback(self.value, value)
        self.value = value

要使用此代码，请创建一个包含应调用函数的对象:

def my_callback(oldVal, newVal):
    print "Value changed from {0} to {1}.".format(oldVal, newVal)

detector = EdgeTrigger(my_callback)

然后在获得每个新值时“调用”该对象:

with open("infile.txt") as f:
    for line in f:
        detector(line.strip())

这将从文件中读取行并在两个连续行不相同时打印一条消息。

$ cat infile.txt 
1
1
1
2
2
1

1
2
2
5
$ python edgedetect.py
Value changed from None to 1.
Value changed from 1 to 2.
Value changed from 2 to 1.
Value changed from 1 to .
Value changed from  to 1.
Value changed from 1 to 2.
Value changed from 2 to 5.