I'm not sure win32gui.EnumWindows is working properly

I think that EnumWindows is doing exactly what its documentation says it will do. Returning False from the callback function terminates the enumeration. Your statement "the wrapper can only sees the return value" means nothing, since according to the documentation this function isn't supposed to return anything. Why don't you forget about analyzing the return value and just wrap the call to EnumWindows in a try: except: block if you want to suppress the exception.