Pouvez-vous m'expliquer comment fonctionne le "other" ?

Question

class Board:

  def __init__(self,other=None):
    self.player = 'X'
    self.opponent = 'O'
    self.empty = ' '
    self.size = 3
    self.fields = {}
    for y in range(self.size):
      for x in range(self.size):
        self.fields[x,y] = self.empty
    # copy constructor
    if other:
        self.__dict__ = deepcopy(other.__dict__)