Why can't I successfully draw the region of interest in a matplotlib color map embedded in a pyqt5 gui?

I'm trying to draw a region of interest on a color map that is embedded in a pyqt5 gui. This is an example of what I want.

import sys
from PyQt5.QtWidgets import (QWidget, QPushButton,
                             QHBoxLayout, QVBoxLayout, QApplication)
from PyQt5 import QtCore
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.backends.backend_qt5agg import NavigationToolbar2QT as NavigationToolbar
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas

import ROI_class as roi # ROI_class.py

class Example(QWidget):

    def __init__(self):
        super().__init__()

        self.initUI()
        self.drawButton.clicked.connect(self.draw_map_Callback)
        self.roiButton.clicked.connect(self.choose_roi)

    def initUI(self):
        self.drawButton = QPushButton("draw map")
        self.roiButton = QPushButton("roi")

        self.hbox = QHBoxLayout()
        self.hbox.addStretch(1)
        self.hbox.addWidget(self.drawButton)
        self.hbox.addWidget(self.roiButton)

        self.vbox = QVBoxLayout()
        self.vbox.addStretch(1)
        self.vbox.addLayout(self.hbox)

        self.setLayout(self.vbox)
        self.setGeometry(500, 500, 500, 500)
        self.setWindowTitle('ROI')
        self.show()
        
    def draw_map_Callback(self):        
        img = np.ones((100, 100)) * range(0, 100)
        fig, ax1 = plt.subplots()
        
        self.con_canvas = FigureCanvas(plt.figure(tight_layout=True))
        self.con_canvas.setFocusPolicy(QtCore.Qt.ClickFocus)
        self.con_canvas.setFocus()
        self.con_toolbar = NavigationToolbar(self.con_canvas, self)
        self.vbox.addWidget(self.con_toolbar)
        self.vbox.addWidget(self.con_canvas)
        self._con_ax = self.con_canvas.figure.subplots()
        self.con_img = self._con_ax.imshow(img, cmap ='jet')
        self._con_ax.set_xlabel('xlabel')
        self._con_ax.set_ylabel('ylabel')
        self.con_cbar = self.con_canvas.figure.colorbar(self.con_img)
        self._con_ax.set_aspect('equal')
        
        
    def choose_roi(self):
        y = roi.new_ROI(self.con_img)

        
if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

It will draw a colormap when I click "draw map". Then I want it to allow me to draw a region of interest with my mouse and get a mask using the code on this link below.

https://github.com/martindurant/misc/blob/master/ROI.py

The "ROI_class" that is imported is just a copy and paste of the code in the link above.

I can successfully draw the plot on the GUI but when I click "roi", it doesn't allow me to draw the region of interest.

When I mad a new file and paste the code in the link above with something like

fig, ax1 = plt.subplots()
s = ax1.imshow(img, cmap ='jet')
ax1.set_xlabel('subcolor')
ax1.set_ylabel('ylabel')
y = new_ROI(s)

at the end of the code, it worked just fine and I was able to draw the region of interest and get the mask of it.

But when I try to do this in the GUI, it wouldn't let me draw the region of interest. I'm very confused why this isn't working.

The problem is that picker (the variable "y") is a local variable that gets destroyed instantly causing the desired behavior not to be executed. The solution is to make it an attribute of the class:

self.y = roi.new_ROI(self.con_img)