numpy - matplotlib.pyplot Event Handling: Linear Increase in Key-Press Dwell Time? -

i writing image processing module in python using matplotlib.pyplot , numpy backend. images largely in tiff format, code below uses tifffile convert 3d image file 4d array in numpy. below code aims move through z-plane of 3d image, 1 image @ time, using z , x hotkeys. problem quite interesting , can't figure out: time between event , action (pressing x , displaying z+1 image) gets twice long each event. timed it, results below: 1st z-press: 0.124 s 2nd z-prss: 0.250 s 3rd z-press: 0.4875 s

it bonafide linear increase, can't find in code bug be.

import matplotlib.pyplot plt import numpy np import tifffile tiff  class image:     def __init__ (self, fname):         self.fname = fname         self.fig = plt.figure()         self.z = 0         self.ax = self.fig.add_subplot(111)         self.npimg = tiff.imread(self.fname)         self.plotimg()         self.connect()      def plotimg(self):         plt.imshow(self.npimg[self.z][0])         plt.show()      def connect(self):         self.cidkeypress = self.fig.canvas.mpl_connect('key_press_event',self.keypress)      def disconnect(self):         self.fig.canvas.mpl_disconnect(self.cidkeypress)      def keypress(self, event):         if event.key == 'x':             self.z += 1             self.plotimg()         elif event.key == 'z':             self.z -= 1         self.plotimg() 

since didn't provide example file, can't test code. think problem is, call plt.imshow() repeatedly. each time new axesimage object added figure. why timings increase linearly.

so solution have 1 axesimage object , update data. adapt __init__ , plotimg follows:

def __init__ (self, fname):     self.fname = fname     self.fig = plt.figure()     self.z = 0     self.ax = self.fig.add_subplot(111)     self.npimg = tiff.imread(self.fname)     self.pltim = plt.imshow(self.npimg[self.z][0])     self.connect()     plt.show()  def plotimg(self):     self.pltim.set_data(self.npimg[self.z][0])     plt.draw() 

beware: untested code!

edit:

difference between plt.imshow , plt.show:

despite similar name, different things: plt.imshow plotting function, draws image current axes (similar plt.plot, plt.scatter, etc.) plt.show however, dispays figure on screen , enters backends mainloop (i.e. blocks code). this answer explains in more detail