code: def _has_init(directory):
      
      mod_or_pack = os.path.join(directory, "__init__")
      for ext in PY_SOURCE_EXTS + ("pyc", "pyo"):
          if os.path.exists(mod_or_pack + "." + ext):
              return mod_or_pack + "." + ext
      return None
docs: if the given directory has a valid __init__ file, return its path,
      else return None