def neighbors(self, i=None, j=None):
""" Construct and return Neighborhood of point if point is exists
"""
if not self.position_exists(i, j):
raise ValueError(
"Position ({}, {}) does not exist in a {} x {} matrix".format(
i, j, self.m, self.n))
if (i is None) != (j is None):
# Only one coordinate provided
raise ValueError("Cannot get neighbors of a column or row")
if i == j == None and self.position is None:
# Both None
raise ValueError(
"Cannot retrieve neighbors. Either set start or provide coordinates to mark."
)
i, j, _ = self.position
nbhd = Neighborhood()
# Keep things ordered clockwise for consistency in code
# Top
if i > 0:
nbhd.top = Position(i - 1, j, self.M[i - 1][j])
# Right
if j < self.n - 1:
nbhd.right = Position(i, j + 1, self.M[i][j + 1])
# Bottom
if i < self.m - 1:
nbhd.bottom = Position(i + 1, j, self.M[i + 1][j])
# Left
if j > 0:
nbhd.left = Position(i, j - 1, self.M[i][j - 1])
return nbhd
