>     - type -- The type which the command-line arguments should be converted
>         to, should be one of 'string', 'int', 'float', 'complex' or a
>         callable object that accepts a single string argument. If None,
>         'string' is assumed.

I misunderstood this sentence in the docstring of arcparse.Action because `bool` or `unicode` is not appeared in this list, which are callables.

So, I close this issue.