Rotate right a 2d array by 90 degrees using constant space usage

rotateArray.py

def rotateSquare(a, start, length):
	lastIndex = start + length - 1
	for i in range(length-1):
		temp = a[start][start + i]
		a[start][start + i] = a[lastIndex - i][start]
		a[lastIndex - i][start] = a[lastIndex][lastIndex - i]
		a[lastIndex][lastIndex - i] = a[start + i][lastIndex]
		a[start + i][lastIndex] = temp

# Rotate right a 2D array by 90 degrees
def rotate2DArray(a):
	i = 0
	squareLength = 	len(a)
	while True:
		rotateSquare(a, i, squareLength)
		i += 1
		squareLength -= 2
		if squareLength < 2:
			break