Question

我尝试绘制从另一个程序转储到csv的实时（和连续）数据源。我得到了绘图工作但后来意识到我的数据只绘制，直到我执行代码。我相信我的解析功能有问题（这种东西有点新）但我无法弄清楚是什么。

SELECT a.id, a.event_id, a.dt_start, min(b.dt_end)
  FROM #starts AS a
  LEFT JOIN #ends AS b
    ON a.id       = b.id
   AND a.event_id = b.event_id
   AND a.dt_start < b.dt_end
   AND DATEDIFF(day, dt_start, dt_end) <= 5  
 GROUP BY a.id, a.event_id, a.dt_start

来自csv的示例行如下所示： import threading import csv import dateutil.parser import datetime import time import matplotlib import matplotlib.pyplot as plt from matplotlib import animation log = "sample.csv" data = "" mytime = "" thickness = "" times = "" #attempt at continuously reading my data source def parser(): with open(log, 'r') as f: global data reader = csv.reader(f, delimiter=',') data = reader.readlines() time_thickness_data = [] while 1: last_pos = f.tell() next_line = f.readline() if not next_line: time.sleep(1) f.seek(last_pos) else: mytime, thickness = splitter(next_line) time_thickness_data.append([mytime, thickness]) def splitter(line): mytime = line[0] thickness = line[3] return (mytime, thickness) times = [] for date in mytime: _ = dateutil.parser.parse(date) times.append(datetime.datetime.strftime(_,'%H')) def main(): a = threading.Thread(target=parser) b = threading.Thread(target=splitter) a.start() b.start() if __name__ == "__main__": main() #goes on to animated plot using times for x axis and thickness for y fig = plt.figure() axes = fig.add_subplot(111) line, = axes.plot([], [], '.') plt.show(block=False) #i had to use this to get my plot to show up def init(): line.set_data([],[]) return line, def animate(i): a = 50 * i xdata = times[:a] ydata = thickness[:a] line.set_data(xdata, ydata) plt.draw() axes.relim() axes.autoscale_view(True,True,True) return line, anim = animation.FuncAnimation(fig, animate, init_func=init, interval=1, blit=True) plt.show()

Answer 1

代码中有太多未使用的部分，无法真正理解您要实现的目标。这是一个简单的函数：

打开csv文件
重复从中读取行，等待到达文件末尾时添加新行

使用每个csv行的解码列表调用回调函数

def csv_process(filename, callback, delay=1):
    class waiter:     # wrapper around a file object to wait for new lines on EOF
        def __init__(self, fd, delay=1):
            self.fd = fd
            self.delay = delay
        def __iter__(self):
            return self
        def next(self):  # try to read a line of wait delay seconds
            while True:
                line = fd.readline()
                if line:
                    return line
                time.sleep(self.delay)
        def __next__(self):  # ensure compatibility with Python3.x
            return self.next()
    with open(filename, "rb") as fd:
        rows = csv.reader(waiter(fd, delay), delimiter=',')
        for row in rows:
            callback(row)

Python2迭代器应实现next，而Python3则应实现__next__。为确保与两者兼容，上面的代码定义了两种方法。

在python中解析数据馈送

1 个答案: