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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def extend_extents(extents, factor=1.1):
 """Extend a given bounding box The bounding box (x1, y1, x2, y2) is centrally stretched by the given factor. :param extents: The bound box extents :param factor: The factor for stretching :return: (x1, y1, x2, y2) of the extended bounding box """

    width = extents[2] - extents[0]
    height = extents[3] - extents[1]
    add_width = (factor - 1) * width
    add_height = (factor - 1) * height
    x1 = extents[0] - add_width / 2
    x2 = extents[2] + add_width / 2
    y1 = extents[1] - add_height / 2
    y2 = extents[3] + add_height / 2
    return x1, y1, x2, y2