Lazy-loading domain map

snippet.py

class DomainMap:
  _domain_map = None
  
  @classmethod
  def _get(cls):
    # do heavy lifting here
    # result = ...
    return result
  
  @classmethod 
  def get(cls):
    if cls._domain_map is None:
      cls._domain_map = cls._get()
    
    return cls._domain_map