A developer reads the Gang of Four (GoF) book and tries to implement a Singleton pattern in Python exactly as described for Java — using a private constructor and a static getInstance() method. Their Python colleague says: "The canonical GoF Singleton implementation doesn't translate idiomatically to Python." What are the two most Pythonic ways to implement a Singleton, and how do they differ from the GoF approach?

# config.py
  class _Config:
      def __init__(self):
          self.db_host = "localhost"
          self.debug = False
  
  # Module-level instance — created once on first import, cached by sys.modules
  config = _Config()
  
  # Usage in any file:
  from config import config
  config.db_host = "production.db.com"  # Same object everywhere