btn.clicked.connect(self.lb_pressed)
def lb_pressed(self):
    sender = self.sender()
    if sender.isEnabled():
        sender.change_color('red')

def mousePressEvent(self, event):
        if event.button() == Qt.LeftButton:
            self.lb_pressed()
        elif event.button() == Qt.RightButton:
            self.rb_pressed()

def rb_pressed(self):
    sender = self.sender()
    if sender.isEnabled():
        sender.change_color('green')

AttributeError: 'NoneType' object has no attribute 'isEnabled'

from PyQt5 import Qt


class MyButton(Qt.QPushButton):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def mousePressEvent(self, event):
        button = event.button()
        if button == Qt.Qt.RightButton:
            print("Right button click!")
            self.setStyleSheet("""QPushButton{
                    background-color: #aaaaff;
                    border: 1px solid black;
                    border-radius: 5px;
                }
                """)
        elif button == Qt.Qt.LeftButton:
            print("Left button click!")
            self.setStyleSheet("""QPushButton{
                    background-color: #ffaaaa;
                    border: 1px solid black;
                    border-radius: 10px;
                }
                """)
        return Qt.QPushButton.mousePressEvent(self, event)


class Widget(Qt.QWidget):

    def __init__(self, *args, **kwargs):
        super().__init__()
        layout = Qt.QGridLayout(self)

        for i in range(8):
            for j in range(8):
                layout.addWidget(MyButton("Button[{}, {}]".format(i, j)), i, j)


if __name__ == '__main__':
    app = Qt.QApplication([])
    w = Widget()
    w.show()
    app.exec()