>>> fd=ast.FunctionDef(name="hi", args=[])
>>> fd
FunctionDef(name='hi', args=[], body=[], decorator_list=[], returns=None, type_comment=None, type_params=[])
>>> fd.__replace__()
Traceback (most recent call last):
  File "<python-input-16>", line 1, in <module>
    fd.__replace__()
    ~~~~~~~~~~~~~~^^
TypeError: FunctionDef.__replace__ missing 2 keyword arguments: 'returns', 'type_comment'.