Calling a method in another class from a matplotlib's custom toolbar's button

I'm using PyQt and Matplotlib libraries to create an application. I've created a sub-class of my QMainWindow and I do not know how to connect the method of the new class to the methods in the first class.

At first, I created a QPushButton in the QMainWindow like this:

class A(QMainWindow):
  def __init__(self):
    QMainWindow.__init__(self)

    self.mainWidget = QWidget()
    self.setCentralWidget(self.mainWidget)

    layout = QVBoxLayout()
    self.mainWidget.setLayout(layout)

    self.figure_canvas = FigureCanvas(Figure(facecolor="lightblue"))
    layout.addWidget(self.figure_canvas, 10)

    self.axes = self.figure_canvas.figure.add_subplot(111)

    #Here is the first button creatd and added to the navigation toolbar
    #using addWidget
    self.btn_selection_tool = QPushButton(QIcon("select.png"), "")
    self.navigation_toolbar.addWidget(self.btn_selection_tool)

    #And here is how i connected this button to two methods
    self.connect(self.btn_selection_tool, SIGNAL("clicked()"), self.method1)
    self.connect(self.btn_selection_tool, SIGNAL("clicked()"), self.method2)

But now, I had to create a new class (class B) and I need to connect a method from this one to the methods called before by the QPushButton in class A. But, in this case, I do not have a button to do it. I just need to "trigger" this methods in class A , by a method in class B.

My problem is that I can not call the methods in class A (self.method1 and self.method2)the same way that I did when I created the QPushbutton. This is before creating the subclass.

I've tried doing:

def method_in_B_class(self):
  self.a  = A()
  self.a.method1()
  self.a.method2()

How can I do this? Hope you can help me.

------ EDIT -----

These are the two methods:

def method1(self):
    self.figure_canvas.setCursor(Qt.IBeamCursor)
    self.selection_mode = None
    #self.selectionmode is a variable that I change when method1 is called
    #and I can go through the "if" in method2

def method2(self):
    #I define some conditions with another variables
    if len(self.axes.lines) >= 1 and self.selection_mode == None and A.send_msg == None:

        self.cid_press = self.figure_canvas.mpl_connect("button_press_event", self.method3)
        self.cid_release = self.figure_canvas.mpl_connect("button_release_event", self.method4)

    elif self.selection_mode == "disable":
        self.disconnect(self)

So, when they are called using:

def method_in_B_class(self):
  self.a  = A()
  self.a.method1()
  self.a.method2()

they are instantiated, but then they are "finished" we might say. This is that the QtCursor does not change, and the method3 and method4 are not called.