>>> print(ast.dump(ast.parse('my_var["key"]["subkey"]'), indent=2))
Module(
  body=[
    Expr(
      value=Subscript(
        value=Subscript(
          value=Name(id='my_var', ctx=Load()),
          slice=Constant(value='key'),
          ctx=Load()),
        slice=Constant(value='subkey'),
        ctx=Load()))],
  type_ignores=[])