pyqt5でコードを少し変えたらkeyPressEventが動作しなくなった

pyqt5で特定のキーを押したときにアクションを起こすグラフは次のようなコードで書けました。

import sys
from PyQt5 import QtGui,QtCore, QtWidgets,QtMultimedia, QtMultimediaWidgets
from PyQt5.QtWidgets import QDialog, QApplication, QVBoxLayout
from PyQt5.QtCore import Qt
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt5 import NavigationToolbar2QT as NavigationToolbar
from matplotlib.figure import Figure
import matplotlib.pyplot as plt

import numpy as np


class MyCanvas(FigureCanvas):
    def __init__(self, parent=None, width=5, height=4, dpi=100):

        fig = Figure(figsize=(width, height), dpi=dpi)
        self.axes = fig.add_subplot(111)

        self.plot_figure()

        FigureCanvas.__init__(self, fig)
        self.setParent(parent)

    def plot_figure(self):
        pass


    def keyPressEvent(self,event):
        if event.key() == Qt.Key_Right:
            print("g")
        else:
            print("G")


class MyStaticMplCanvas(MyCanvas):
    def __init__(self, parent=None):
        super(MyStaticMplCanvas,self).__init__(parent)
        self.setFocusPolicy(Qt.StrongFocus)

    def plot_figure(self):
        x=np.arange(0,2*np.pi,0.1)
        y=np.sin(x)
        self.axes.plot(x,y,"-")
        self.axes.set_xlabel("x")
        self.axes.set_ylabel("y")
        self.axes.set_xlim(0,2*np.pi)     



class Main(QDialog):
    def __init__(self, parent=None):
        super(Main, self).__init__(parent)

        canvas = MyStaticMplCanvas(self)

        layout = QVBoxLayout()
        layout.addWidget(canvas)

        self.setLayout(layout)

        self.setWindowTitle('plot')
        self.show()



if __name__ == '__main__':
    app = QApplication(sys.argv)
    win = Main()

    app.exec_()

これを実行すると次のようなGUIが作成されます。

ここで、グラフのプロットをMyStaticMplCanvasで別クラスに分けるのも冗長と思い、次のようにMyCanvasクラスに一つにまとめてみました。

import sys
from PyQt5 import QtGui,QtCore, QtWidgets,QtMultimedia, QtMultimediaWidgets
from PyQt5.QtWidgets import QDialog, QApplication, QVBoxLayout
from PyQt5.QtCore import Qt
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.backends.backend_qt5 import NavigationToolbar2QT as NavigationToolbar
from matplotlib.figure import Figure
import matplotlib.pyplot as plt

import numpy as np


class MyCanvas(FigureCanvas):
    def __init__(self, parent=None, width=5, height=4, dpi=100):
        super(MyCanvas,self).__init__(parent)
        self.setFocusPolicy(Qt.StrongFocus)
        fig = Figure(figsize=(width, height), dpi=dpi)
        self.axes = fig.add_subplot(111)

        self.plot_figure()

        FigureCanvas.__init__(self, fig)
        self.setParent(parent)

    def plot_figure(self):
        x=np.arange(0,2*np.pi,0.1)
        y=np.sin(x)
        self.axes.plot(x,y,"-")
        self.axes.set_xlabel("x")
        self.axes.set_ylabel("y")
        self.axes.set_xlim(0,2*np.pi)     


    def keyPressEvent(self,event):
        if event.key() == Qt.Key_Right:
            print("g")
        else:
            print("G")


class Main(QDialog):
    def __init__(self, parent=None):
        super(Main, self).__init__(parent)

        canvas = MyCanvas(self)

        layout = QVBoxLayout()
        layout.addWidget(canvas)

        self.setLayout(layout)

        self.setWindowTitle('plot')
        self.show()



if __name__ == '__main__':
    app = QApplication(sys.argv)
    win = Main()

    app.exec_()

すると、次のようなエラーが出ました。

  File "C:\Users\toma\Anaconda3\lib\site-packages\matplotlib\backends\backend_qt5.py", line 236, in __init__
    figure._original_dpi = figure.dpi

AttributeError: 'Main' object has no attribute 'dpi'

何が悪かったのでしょうか。