'transform : transform from the image coordinate (which will be
the transData of the axes to the world coordinate.
or transform = (transform_xy, inv_transform_xy)
locator1, locator2 : grid locator for 1st and 2nd axis.'

def __init__(self, transform, extreme_finder=None, grid_locator1=None, grid_locator2=None, tick_formatter1=None, tick_formatter2=None):

    if (extreme_finder is None):
        extreme_finder = ExtremeFinderSimple(20, 20)
    if (grid_locator1 is None):
        grid_locator1 = MaxNLocator()
    if (grid_locator2 is None):
        grid_locator2 = MaxNLocator()
    if (tick_formatter1 is None):
        tick_formatter1 = FormatterPrettyPrint()
    if (tick_formatter2 is None):
        tick_formatter2 = FormatterPrettyPrint()
    super(GridFinder, self).__init__(extreme_finder, grid_locator1, grid_locator2, tick_formatter1, tick_formatter2)
    self.update_transform(transform)
