How do you run Matplotlib in another thread on PyQt

Question

I need to display some charts in my PyQt application, so I write down these code. It is works, but sometimes, draw a chart will spend a lot of time, it will "freeze" the main window.

I think do it in another thread should resolved it. But how can I do it? Or, there is another way to draw a chart in "non-block" mode?

from PyQt4 import QtGui
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas   
from matplotlib.figure import Figure

class MplCanvas(FigureCanvas):

    def __init__(self):
        self.fig = Figure()
        self.axes = self.fig.add_subplot(111)

        # do something...
        FigureCanvas.__init__(self, self.fig)
        FigureCanvas.setSizePolicy(self, QtGui.QSizePolicy.Expanding, QtGui.QSizePolicy.Expanding)
        FigureCanvas.updateGeometry(self)
        # do something...

    def draw(self):
        # do something...

Answer 1

You should us QThreads in your Qt application (to make the frame work do all of the hard work for you)

1. put your time consuming work in a worker class (that is derived from QObject)

2. In you class that is caling the plotting add something like

   self.thread = QtCore.QThread(parent=self)
   
   self.worker = Worker(parent=None)
   self.worker.moveToThread(self.thread)
   self.thread.start()
   

and communicate with your worker via signals/slots. If you call it directly (as in self.worker.do_slow_stuff()), it will run on the thread you call it from, which will block the main event loop making the interface freeze.

A good explanation of how to (and not to) do threading with QThread (read both..the first one now describes the default behaviour)