button_press_event in tkinter (only left mouse click)

I am trying to create a UI, which has several subplots as outputs. Then when they one of them is clicked it zooms in on the plot, and when you click again it zoom out.

For this I use the following code:

class ZoomingSubplots(object):
    def __init__(self, fig, *args, **kwargs):
        self.fig, self.axes = fig, fig.subplots(*args, **kwargs)
        self._zoomed = False
        self.fig.canvas.mpl_connect('button_press_event', self.on_click)

    def zoom(self, selected_ax):
        for ax in self.axes.flat:
            ax.set_visible(False)
        self._original_size = selected_ax.get_position()
        selected_ax.set_position([0.05, 0.07, 0.90, 0.80])
        selected_ax.set_visible(True)
        self._zoomed = True        

    def unzoom(self, selected_ax):
        selected_ax.set_position(self._original_size)
        for ax in self.axes.flat:
            ax.set_visible(True)
        self._zoomed = False

    def on_click(self, event):
        if event.inaxes is None:
            return
        if self._zoomed:
            self.unzoom(event.inaxes)
        else:
            self.zoom(event.inaxes)
        self.fig.canvas.draw()

And this works great. However, one thing I don't like is that this will happen even if it is a right-click on the mouse. Is there any way to only make this happen when the left mouse button is clicked, or...?