This doesn't look like Python literal. And if the function accepts a one particular non-literal the user can except that it accepts other looking similarly non-literal, that is false.

Actually ast.literal_eval("+True") is error. But ast.literal_eval(ast.UnaryOp(ast.UAdd(), ast.Constant(True))) is successful by oversight.

And look at this from other side. What is the benefit of accepting "+True"? This doesn't make the code simpler.