python matplotlib graph

python_plot_ping.py

import sys, os, random
from PyQt4.QtCore import *
from PyQt4.QtGui import *

import matplotlib
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt4agg import NavigationToolbar2QTAgg as NavigationToolbar
from matplotlib.figure import Figure

import subprocess
import re

class AppForm(QMainWindow):
    def __init__(self, parent=None):
        QMainWindow.__init__(self, parent)
        self.data = []
        self.setWindowTitle('Ping google result')
        self.create_main_frame()
        self.on_draw()
        self.timer = QTimer()
        self.timer.timeout.connect(self.ping)
        self.timer.start(1000)

    def on_draw(self):
        self.axes.clear()
        self.axes.grid(True)

        self.axes.plot(self.data)

        self.canvas.draw()

    def create_main_frame(self):
        self.main_frame = QWidget()

        self.dpi = 100
        self.fig = Figure((5.0, 4.0), dpi=self.dpi)
        self.canvas = FigureCanvas(self.fig)
        self.canvas.setParent(self.main_frame)

        self.axes = self.fig.add_subplot(111)

        self.mpl_toolbar = NavigationToolbar(self.canvas, self.main_frame)

        vbox = QVBoxLayout()
        vbox.addWidget(self.canvas)
        vbox.addWidget(self.mpl_toolbar)

        self.main_frame.setLayout(vbox)
        self.setCentralWidget(self.main_frame)

    def ping(self):
        host = "www.google.com"
        ping = subprocess.Popen(
            ["ping", "-c", "1", host],
            stdout = subprocess.PIPE,
            stderr = subprocess.PIPE
        )
        out, error = ping.communicate()
        m = re.search('time=(.*)ms', out)
        self.data.append(float(m.group(1)))
        self.on_draw()

def main():
    app = QApplication(sys.argv)
    form = AppForm()
    form.show()
    app.exec_()

if __name__ == "__main__":
    main()