py3compat.py in IPython 1.0.0 has bad references to str_to_unicode.
It is fixed on GitHub.
https://github.com/ipython/ipython/commit/5d0152fce3cee0e5a3d07bb7eb8a78e0b180854e#IPython/utils/py3compat.py
(UPDATE 2013-09-10 13:32 JST)
Fixed in release 1.1.0.
https://github.com/ipython/ipython/blob/rel-1.1.0/IPython/utils/py3compat.py#L62-L70