myPlugin.py

class ThePlugin:
  """My custom plugin for mypy."""
  
  def get_type_analyze_hook(self, fullname: str) -> Optional[Callable[[AnalyzeTypeContext], Type]]:
    """Customize analysis of specific types."""
    if fullname == 'somemodule.SomeName':
      return analyze_some_name
    return None    # mypy will just move on without us.


def analyze_some_name(ctx: AnalyzeTypeContext) -> Type:
  """The name 'somemodule.SomeName' just refers to str."""
  return ctx.api.named_type('builtins.str')


def plugin(version: str) -> Type[JSONSchemaPlugin]:
    """See `https://mypy.readthedocs.io/en/latest/extending_mypy.html`_."""
    return JSONSchemaPlugin

mypy.ini

[mypy]
plugins = myPlugin.py