# Last edited on 2021-07-31 11:45:35 by jstolfi

def ixdiff(u, v):
  # Assumes that {u} and {v} are points of some {d}-dimesnional grid.
  # Returns the number of positions in which they differ.
  # If either of them is {None}, returns 0.
  if u == None or v == None:
    nd = 0
  else:
    nu = len(u); assert len(v) == nu, "incompatible lengths."
    nd = 0; # Count of differences.
    for k in range(nu):
      if u[k] != v[k]: nd += 1
  return nd
  # ----------------------------------------------------------------------