I create a Sudoku game in Python.
I have a:

• Cell class – that “holds” the number possibilities
• Cell groups – that holds the cell class instances

I use the groups to run row, col and square functionalities in Sudoku.
Each cell contains all the groups, he belongs to

class Cell:
   def __init__(groups):
      self.groups = groups

class Group:
   def __init__(cells):
      self.cells = cells

In this case, I can send a chain reaction when a cell value is changed to all relevent cells via their groups.

Is it a good practice to use cross reference between classes in this manner?