python function to extract the values around the border of an array

border.py

def border(array, corner=0, direction='cw'):
    """
    Extract the values arround the border of a 2d array.
    
    Default settings start from top left corner and move clockwise. 
    Corners are only used once.
    
    Parameters
    ----------
    array : array_like
        A 2d array
    corner : {0, 1, 2, 3}
        Specify the corner to start at.
        0 - start at top left corner (default)
        1 - start at top right corner
        2 - start at bottom right corner
        3 - start at bottom left corner
    direction : {'cw', 'ccw'}
        Specify the direction to walk around the array
        cw  - clockwise (default)
        ccw - counter-clockwise
    
    Returns
    -------
    border : ndarray
        Values around the border of `array`.
    
    Examples
    --------
    >>> x, y = np.meshgrid(range(1,6), range(5))
    >>> array=x*y
    >>> array[0,0]=999
    array([[999,   0,   0,   0,   0],
           [  1,   2,   3,   4,   5],
           [  2,   4,   6,   8,  10],
           [  3,   6,   9,  12,  15],
           [  4,   8,  12,  16,  20]])
    >>> border(array)
    array([999,   0,   0,   0,   0,   5,  10,  15,  20,  16,  12,   8,   4,
             3,   2,   1, 999])
    >> border(array, corner=2)
    array([ 20,  16,  12,   8,   4,   3,   2,   1, 999,   0,   0,   0,   0,
             5,  10,  15,  20])
    >>> border(array, direction='ccw')
    array([999,   1,   2,   3,   4,   8,  12,  16,  20,  15,  10,   5,   0,
             0,   0,   0, 999])
    >>> border(array, corner=2, direction='ccw')
    array([ 20,  15,  10,   5,   0,   0,   0,   0, 999,   1,   2,   3,   4,
             8,  12,  16,  20])
    """
    if corner > 0:
        # Rotate the array so we start on a different corner
        array = np.rot90(array, k=corner)
    if direction is 'ccw':
        # Transpose the array so we march around counter-clockwise
        array = array.T

    border = []
    border += list(array[0, :-1])    # Top row (left to right), not the last element.
    border +=list(array[:-1, -1])    # Right column (top to bottom), not the last element.
    border +=list(array[-1, :0:-1])  # Bottom row (right to left), not the last element.
    border +=list(array[::-1, 0])    # Left column (bottom to top), all elements element.
    # NOTE: in that last statement, we include the last element to close the path.

    return np.array(border)