处理多个IO错误

Question

我在课堂上执行了几个IO操作，但这些操作在IOError中经常失败。我想要做的是延迟几百毫秒，然后再试一次，直到成功或某些特定的超时。在继续/结束循环之前，如何确保每个单独的命令都成功？我假设有一种更好的方法来检查所有命令是否成功，而不是为每一项设置一个if语句和一个计数器。

下面我的当前代码经常在IOError中失败，并挂起应用程序的其余部分。

   def __init__(self):
      print("Pressure init.")
      self.readCoefficients()

   def readCoefficients(self):
      global a0_MSB;
      global a0_LSB;
      global b1_MSB;
      global b1_LSB;
      global b2_MSB;
      global b2_LSB;
      global c12_MSB;
      global c12_LSB;

      a0_MSB = Pressure.bus.read_byte_data(Pressure.MPL115A2_ADDRESS,Pressure.MPL115A2_REGISTER_A0_COEFF_MSB+0);
      a0_LSB = Pressure.bus.read_byte_data(Pressure.MPL115A2_ADDRESS,Pressure.MPL115A2_REGISTER_A0_COEFF_LSB+0);

      b1_MSB = Pressure.bus.read_byte_data(Pressure.MPL115A2_ADDRESS,Pressure.MPL115A2_REGISTER_B1_COEFF_MSB+0);
      b1_LSB = Pressure.bus.read_byte_data(Pressure.MPL115A2_ADDRESS,Pressure.MPL115A2_REGISTER_B1_COEFF_LSB+0);

      b2_MSB = Pressure.bus.read_byte_data(Pressure.MPL115A2_ADDRESS,Pressure.MPL115A2_REGISTER_B2_COEFF_MSB+0);
      b2_LSB = Pressure.bus.read_byte_data(Pressure.MPL115A2_ADDRESS,Pressure.MPL115A2_REGISTER_B2_COEFF_LSB+0);

      c12_MSB = Pressure.bus.read_byte_data(Pressure.MPL115A2_ADDRESS,Pressure.MPL115A2_REGISTER_C12_COEFF_MSB+0);
      c12_LSB = Pressure.bus.read_byte_data(Pressure.MPL115A2_ADDRESS,Pressure.MPL115A2_REGISTER_C12_COEFF_LSB+0);

Answer 1

如果您可以逐个读取所有文件，则可以使用一个简单的函数。

import time

# ...

def readCoefficients(self):
    global a0_MSB;
    global a0_LSB;
    global b1_MSB;
    global b1_LSB;
    global b2_MSB;
    global b2_LSB;
    global c12_MSB;
    global c12_LSB;

    max_retries = 15

    a0_MSB = self.readretry(Pressure.MPL115A2_REGISTER_A0_COEFF_MSB+0, max_retries)
    a0_LSB = self.readretry(Pressure.MPL115A2_REGISTER_A0_COEFF_LSB+0, max_retries)

    b1_MSB = self.readretry(Pressure.MPL115A2_REGISTER_B1_COEFF_MSB+0, max_retries)
    b1_LSB = self.readretry(Pressure.MPL115A2_REGISTER_B1_COEFF_LSB+0, max_retries)

    b2_MSB = self.readretry(Pressure.MPL115A2_REGISTER_B2_COEFF_MSB+0, max_retries)
    b2_LSB = self.readretry(Pressure.MPL115A2_REGISTER_B2_COEFF_LSB+0, max_retries)

    c12_MSB = self.readretry(Pressure.MPL115A2_REGISTER_C12_COEFF_MSB+0, max_retries)
    c12_LSB = self.readretry(Pressure.MPL115A2_REGISTER_C12_COEFF_LSB+0, max_retries)

    def readretry(self, address, max_retries):
        for i in range(max_retries):
            try:
                return Pressure.bus.read_byte_data(
                    Pressure.MPL115A2_ADDRESS,
                    address
                )
            except IOError as e:
                # print(e)
                time.sleep(0.1)
        else:
            raise IOError("Reading failed after multiple tries")

注意:您不应该使用globals，尤其是在类中。

Answer 2

你是想独立地还是集体地重新尝试最后8行中的每一行？如果独立地想要创建一个小助手函数：

def retry_function(tries, function, *args, **kwargs):
    for try in range(tries):
        try:
            return function(*args, **kwargs)
        except IOError as e:
            time.sleep(.005)
    raise e   # will be the last error from inside the loop. be sure tries is at least 1 or this will be undefined!

那就这样说吧：

a0_MSB = retry_function(5, Pressure.bus.read_byte_data, Pressure.MPL115A2_ADDRESS,Pressure.MPL115A2_REGISTER_A0_COEFF_MSB+0)

如果不是独立的，而是作为一个组，您可能仍然需要这个助手函数。但是您必须重写它以处理函数/参数的列表，或者传入另一个自定义函数

Answer 3

这是另一种方法。此代码尝试读取所有地址，并保存失败地址。然后稍等，然后重试所有失败的地址，直到正确读取所有地址或超出允许重试次数为止。

def readCoefficients(self):
    (
        a0_MSB, a0_LSB,
        b1_MSB, b1_LSB,
        b2_MSB, b2_LSB,
        c12_MSB, c12_LSB) = self.mio_read(15,
            Pressure.MPL115A2_REGISTER_A0_COEFF_MSB+0,
            Pressure.MPL115A2_REGISTER_A0_COEFF_LSB+0,
            Pressure.MPL115A2_REGISTER_B1_COEFF_MSB+0,
            Pressure.MPL115A2_REGISTER_B1_COEFF_LSB+0,
            Pressure.MPL115A2_REGISTER_B2_COEFF_MSB+0,
            Pressure.MPL115A2_REGISTER_B2_COEFF_LSB+0,
            Pressure.MPL115A2_REGISTER_C12_COEFF_MSB+0,
            Pressure.MPL115A2_REGISTER_C12_COEFF_LSB+0
    )

def mio_read(self, max_retries, *addresses):
    # Create storage for results
    results = [None] * len(addresses)
    # Keep track of the index of a particular address in the list of results
    ios = list(enumerate(addresses))
    for i in range(max_retries):
        failedios = []
        for index, address in ios:
            try:
                results[index] = Pressure.bus.read_byte_data(
                    Pressure.MPL115A2_ADDRESS,
                    address
                )
            except IOError as e:
                # Place address in the queue for the next round
                failedios.append((index, address))
        # If all succeeded
        if len(failedios) == 0:
            return results
        # Time may be reduced as so was spent checking other addresses
        time.sleep(0.1)
        ios = failedios
    else:
        raise IOError(",".join((addr for ind, addr in failedios)))