Problem with event handling in matplotlib in tkinter

Dear all,

I have a problem with using certain class methods as event handlers. In the
following example:

the method Test.on_press() is never executed. Only "clicked0" and "clicked1"
is printed when I click on the canvas. When i use pure matplotlib widgets
instead of tkinter embedding, the code works as expected. Is this a
matplotlib bug or am I doing something wrong?
My software versions are:
Python 3.4.0
matplotlib.__version__ == '1.3.1'
tkinter.TkVersion == 8.6

in Ubuntu 14.04

Thanks in advance for any help,
Stepan

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I have a little update on the issue: I tried it with different versions of
python and matplotlib and it is still present in
python 2.7.6 + matplotlib 1.4.2

but it works as expected in
python 3.4.0 + matplotlib 1.4.2

Should this be reported as a bug in matplotlib 1.4.2 on python 2.7.6?

BTW, I noticed that my minimal text from previous mail didn't get through to
the mailing list, so I am attaching it again (modified for python 2.7)
without formatting:

from __future__ import print_function
import sys
if sys.version_info < (3, 0):
    import Tkinter as tk
else:
    import tkinter as tk
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
import matplotlib.figure as mplfig

class Test:
    def on_press(self, event):
        print("clicked2")

    def connect(self, canvas):
        self.cidpress = canvas.mpl_connect(
                'button_press_event', self.on_press)
        self.cidpress = canvas.mpl_connect(
                'button_press_event', lambda event: print("clicked1"))

class App(object):
    def on_press(self, event):
        print("clicked0")
    def __init__(self, master):
        self.fig = mplfig.Figure()
        self.canvas = FigureCanvasTkAgg(self.fig, master=master)

        dl = Test()
        dl.connect(self.canvas)

        self.cidpress = self.canvas.mpl_connect(
                'button_press_event', self.on_press)

        self.canvas.get_tk_widget().pack()
        self.canvas.draw()

if __name__ == "__main__":
    root = tk.Tk()
    app = App(root)
    tk.mainloop()

this should print
clicked2
clicked1
clicked0

after each click on the canvas. But in python 2.7.6 it prints only
clicked1
clicked0

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I think it is because your Test() class is not subclassed from “object”. Of course, I have no clue why that would be an issue, but I have seen stranger things when not subclassing from object.

···

On Fri, Nov 7, 2014 at 9:31 AM, rouckas <stepan.roucka@…287…> wrote:

I have a little update on the issue: I tried it with different versions of

python and matplotlib and it is still present in

python 2.7.6 + matplotlib 1.4.2

but it works as expected in

python 3.4.0 + matplotlib 1.4.2

Should this be reported as a bug in matplotlib 1.4.2 on python 2.7.6?

BTW, I noticed that my minimal text from previous mail didn’t get through to

the mailing list, so I am attaching it again (modified for python 2.7)

without formatting:

from future import print_function

import sys

if sys.version_info < (3, 0):

import Tkinter as tk

else:

import tkinter as tk

from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg

import matplotlib.figure as mplfig

class Test:

def on_press(self, event):

    print("clicked2")



def connect(self, canvas):

    self.cidpress = canvas.mpl_connect(

            'button_press_event', self.on_press)

    self.cidpress = canvas.mpl_connect(

            'button_press_event', lambda event: print("clicked1"))

class App(object):

def on_press(self, event):

    print("clicked0")

def __init__(self, master):

    self.fig = mplfig.Figure()

    self.canvas = FigureCanvasTkAgg(self.fig, master=master)



    dl = Test()

    dl.connect(self.canvas)



    self.cidpress = self.canvas.mpl_connect(

            'button_press_event', self.on_press)



    self.canvas.get_tk_widget().pack()

    self.canvas.draw()

if name == “main”:

root = tk.Tk()

app = App(root)

tk.mainloop()

this should print

clicked2

clicked1

clicked0

after each click on the canvas. But in python 2.7.6 it prints only

clicked1

clicked0

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Thanks for the tip. However, subclassing from object didn't help.

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Figured it out! The instance of Test() isn’t being retained anywhere, so when it goes out of scope, the garbage collector eventually gets it. The fact that it works in py3k is likely a coincidence as the garbage collector would eventually have cleaned it up at some point. I don’t know the scoping/garbage collection rules for lambdas, so I am guessing that they persist as they are part of the code as opposed to a de-reference-able (is that even a word?). Just save the instance of Test as a member variable of App, and you should be good to go!

Ben Root

···

On Fri, Nov 7, 2014 at 10:05 AM, rouckas <stepan.roucka@…985…> wrote:

Thanks for the tip. However, subclassing from object didn’t help.

View this message in context: http://matplotlib.1069221.n5.nabble.com/Problem-with-event-handling-in-matplotlib-in-tkinter-tp44302p44315.html
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This note in cbook.py (which handles the callback registry) explains it. . . sort of:

In practice, one should always disconnect all callbacks when they
are no longer needed to avoid dangling references (and thus memory
leaks). However, real code in matplotlib rarely does so, and due
to its design, it is rather difficult to place this kind of code.
To get around this, and prevent this class of memory leaks, we
instead store weak references to bound methods only, so when the
destination object needs to die, the CallbackRegistry won't keep
it alive. The Python stdlib weakref module can not create weak
references to bound methods directly, so we need to create a proxy
object to handle weak references to bound methods (or regular free
functions). This technique was shared by Peter Parente on his
`"Mindtrove" blog
<http://mindtrove.info/articles/python-weak-references/>`_.

  Definitely a hidden trap!

  Also, speaking of the dangers of classes not inheriting from object, I noticed that CallbackRegistry in cbook.py is also an old-style class (doesn't inherit from object). I then did a search and found numerous old-style classes throughout MPL. Is there any reason for this?

···

On 2014-11-07 09:37, Benjamin Root wrote:

Figured it out! The instance of Test() isn't being retained anywhere, so
when it goes out of scope, the garbage collector eventually gets it. The
fact that it works in py3k is likely a coincidence as the garbage
collector would eventually have cleaned it up at some point. I don't
know the scoping/garbage collection rules for lambdas, so I am guessing
that they persist as they are part of the code as opposed to a
de-reference-able (is that even a word?). Just save the instance of Test
as a member variable of App, and you should be good to go!

--
Brendan Barnwell
"Do not follow where the path may lead. Go, instead, where there is no path, and leave a trail."
    --author unknown

It works. Thanks a lot for explanation, Ben.

Stepan

···

On Fri, Nov 7, 2014 at 6:37 PM, Benjamin Root <ben.root@…1304…> wrote:

Figured it out! The instance of Test() isn’t being retained anywhere, so when it goes out of scope, the garbage collector eventually gets it. The fact that it works in py3k is likely a coincidence as the garbage collector would eventually have cleaned it up at some point. I don’t know the scoping/garbage collection rules for lambdas, so I am guessing that they persist as they are part of the code as opposed to a de-reference-able (is that even a word?). Just save the instance of Test as a member variable of App, and you should be good to go!

Ben Root

On Fri, Nov 7, 2014 at 10:05 AM, rouckas <stepan.roucka@…287…> wrote:

Thanks for the tip. However, subclassing from object didn’t help.

View this message in context: http://matplotlib.1069221.n5.nabble.com/Problem-with-event-handling-in-matplotlib-in-tkinter-tp44302p44315.html
Sent from the matplotlib - users mailing list archive at Nabble.com.



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