PyQt4, matplotlib, modifying the axis labels of an existing plot

Question

I'm creating plots in PyQt4 and matplotlib. The following oversimplified demo program shows that I want to change the label on an axes in response to some event. For demonstrating here I'm made that a "pointer enter" event. The behavior of the program is that I simply don't get any change in the appearance of the plot.

import sys
from PyQt4.QtGui import *
from PyQt4.QtCore import *
from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
import matplotlib.pyplot as plt
import random


class Window(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setMinimumSize(400,400)
        # set up a plot but don't label the axes
        self.figure = plt.figure()
        self.canvas = FigureCanvas(self.figure)
        self.axes = self.figure.add_subplot(111)
        h = QHBoxLayout(self)
        h.addWidget(self.canvas)

    def enterEvent(self, evt):
        # defer labeling the axes until an 'enterEvent'. then set
        # the x label
        r = int(10 * random.random())
        self.axes.set_xlabel(str(r))


if __name__ == "__main__":
    app = QApplication(sys.argv)
    w = Window()
    w.show()
    app.exec_()

three_pineapples · Accepted Answer · 2013-10-16 03:12:13Z

2

You are almost there. You just need to instruct matplotlib to redraw the plot once you have finished calling functions like set_xlabel().

Modify your program as follows:

def enterEvent(self, evt):
    # defer labeling the axes until an 'enterEvent'. then set
    # the x label
    r = int(10 * random.random())
    self.axes.set_xlabel(str(r))
    self.canvas.draw()

You will now see the label change each time you move the mouse into the window!

answered Oct 16, 2013 at 3:12

three_pineapples

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2 Comments

composerMike Over a year ago

Thanks. In general under what conditions does draw() need to be called to update the appearance of the plot?

Rodrigo Over a year ago

If anyone stumbles upon this, I had a similar problem: my axes labels wouldn't show up even though I was calling set_xlabel. Turned out it was an ordering problem, set_xlabel must be called after the data has been drawn.

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