The code works fine on 3.2.2, Win7, IDLE, narrowest window possible (about 14 chars), which actually wraps to the window width. (In command window, lines are fixed length and scroll bar is added if window is narrowed.) What system and version are you running? 

The error directly comes from textwrap. In the other hand, textwrap.wrap works with widths down to 1 (on 3.2.2), which suggests that argparse is calling it wrong. Except that it is not on my system. 

Could you add 'print(width)' before the call to textwrap
    return _textwrap.wrap(text, width)
to see if -1 is being passed?