Question

我希望让我的Python（2.7.5）脚本连续读取并解析来自连续子进程的时间戳和其他信息，对系统时间进行时间戳比较，并将其写入文本文件。我将通过EPICS频道访问过程调用camonitor实用程序。这类似于top这样的行为，它将持续运行并更新数据，直到进程被杀死为止。谷歌搜索并浏览了许多帖子后，这就是我的意思。我想我缺少将数据连续添加到文本文件的东西。

import subprocess
from Queue import Queue, Empty
from threading import Thread
from datetime import datetime
import time

class NonBlockingStreamReader:

    def __init__(self, stream):
        '''
        stream: stream to read from such as stdout
        '''
        self._s = stream
        self._q = Queue()

        def _populateQueue(stream, queue):
            '''
            collect lines from 'stream' and put them in 'queue'
            '''
            while True:
                line = stream.readline()
                if line:
                    queue.put(line)
                else:
                    raise UnexpectedEndOfStream

        self._t = Thread(target = _populateQueue, args = (self._s, self._q))
        self._t.daemon = True
        self._t.start() # start collecting lines from thel stream

    def readline(self, timeout = None):
        try:
            return self._q.get(block = timeout is not None, timeout = timeout)

        except Empty:
            return None


class UnexpectedEndOfStream(Exception): pass

def caMonitor(signalList):

     cmd = ["camonitor"]
     # add signals to the camonitor command
     cmd.extend(signalList)

     print(cmd)

     process = subprocess.Popen(cmd, stdout=subprocess.PIPE)
     # wrap process.stdout with a NonBlockingStreamReader object:
     nbsr = NonBlockingStreamReader(process.stdout)

     # get the output for  X seconds
     t_end = time.time() + 1

     fmt = "%H:%M:%S.%f"

     while time.time() < t_end:
        try:
              output = nbsr.readline(0.05)
              # 0.05 secs to get the results
              '''
              if not output:
                 print ('[No data]')
                 break
              '''
              signal = output[0:16]
              timestamp = output[42:57]
              now = datetime.now()
              sysTime = now.strftime("%H:%M:%S.%f")

              tstamp1 = datetime.strptime(timestamp, fmt)
              tstamp2 = datetime.strptime(sysTime, fmt)

              if tstamp1 > tstamp2:
                 td = tstamp1 - tstamp2
              else:
                 td = tstamp2 - tstamp1

              print(signal + ' ' + timestamp + ' systime ' + sysTime + ' delta: ' + str(td))

              with open('camonlog.log', 'a+') as f:
                 f.write(signal + ' ' + timestamp + ' systime ' + sysTime + ' delta: ' + str(td) + '\n')

        except TypeError:
              print "no data"

Answer 1

在类 NonBlockingStreamReader 中，如果流中没有任何数据，populateQueue方法将仅引发UnexpectedEndOfStream异常，并且该线程将终止并且不会监视您的流。

因此定义这样的方法：

def _populateQueue(stream, queue):
    while True:
        line = stream.readline()
        if line:
            queue.put(line)
        else:
            time.sleep(1)

解析连续子过程并用Python写入文件

1 个答案: