def area_of_rectangle(height, width = None):
    """
    Returns the area of a rectangle.

    Parameters
    ----------
    height : int or float 
        The height of the rectangle.
    width : int or float
        The width of the rectangle. If `None` width is assumed to be equal to 
        the height.

    Returns
    -------
    int or float
        The area of the rectangle

    Examples
    --------
    >>> area_of_rectangle(7)
    49
    >>> area_of_rectangle (7, 2)
    14
    """
    area = height * width
    return area