title: Live Plotting with PyQtGraph in PyQt4
body: <p>I am quite new in Python and TRYING to make a PyQt4 app, where I am embedding PyQtGraph in it. I've got this PyQtGraph live plotter that works fantastically: </p>
  
  <pre><code>from pyqtgraph.Qt import QtGui, QtCore
  import pyqtgraph as pg
  import random
  
  app = QtGui.QApplication([])
  p = pg.plot()
  curve = p.plot()
  data = [0]
  
  def updater():
  
      data.append(random.random())
      curve.setData(data) #xdata is not necessary
  
  
  timer = QtCore.QTimer()
  timer.timeout.connect(updater)
  timer.start(0)
  
  if __name__ == '__main__':
      import sys
      if (sys.flags.interactive != 1) or not hasattr(QtCore, 'PYQT_VERSION'):
          QtGui.QApplication.instance().exec_()
  </code></pre>
  
  <p>For embedding in a bigger PyQt4 app, I need a layout for including a pyqtgraph.PlotWidget(). For that matter I set a centralWidget in my MainWindow. I create a button, that should start plotting just as the previous code does, but just nothing happens when I call the updater function through the plotter function:</p>
  
  <pre><code>import sys
  from PyQt4 import QtCore, QtGui
  import pyqtgraph as pg
  import random
  
  class MainWindow(QtGui.QMainWindow):
      def __init__(self, parent=None):
          super(MainWindow, self).__init__(parent)
          self.central_widget = QtGui.QStackedWidget()
          self.setCentralWidget(self.central_widget)
          login_widget = LoginWidget(self)#to say where the button is
          login_widget.button.clicked.connect(self.plotter)
          self.central_widget.addWidget(login_widget)
  
      def plotter(self):
          self.data =[0]
          timer = QtCore.QTimer()
          timer.timeout.connect(self.updater)
          timer.start(0)
  
      def updater(self):
  
          self.data.append(random.random())
          plot.setData(self.data)
  
  class LoginWidget(QtGui.QWidget):
      def __init__(self, parent=None):
          global plot
          super(LoginWidget, self).__init__(parent)
          layout = QtGui.QHBoxLayout()
          self.button = QtGui.QPushButton('Start Plotting')
          layout.addWidget(self.button)
          plot = pg.PlotWidget()
          layout.addWidget(plot)
          self.setLayout(layout)
  
  if __name__ == '__main__':
      app = QtGui.QApplication([])
      window = MainWindow()
      window.show()
      app.exec_()
  </code></pre>
  
  <p>Is nothing happening because I have to thread? </p>