The sphinx latex output uses facychap Bjarne style by default (see comments to question). I did not like the default layout, especially the fonts did not suite my book. Once I found out how to modify facychap I was able to make the layout changes to the preamble (in conf.py). Here is what I did:
% load BebasNeue font
\pdfmapfile{lcdftools.map}
% use BebasNeue font for headings
\titleformat{\section}
{\fontfamily{BebasNeue}\selectfont\LARGE}
{\thesection}{1em}{}
\titleformat{\subsection}
{\fontfamily{BebasNeue}\selectfont\large}
{\thesubsection}{1em}{}
% modifications to the the part page
\makeatletter
\def\@part[#1]#2{%
\ifnum \c@secnumdepth >-2\relax
\refstepcounter{part}%
\addcontentsline{toc}{part}{\thepart\hspace{1em}#1}%
\else
\addcontentsline{toc}{part}{#1}%
\fi
\markboth{}{}%
{\centering
\interlinepenalty \@M
\normalfont
\ifnum \c@secnumdepth >-2\relax
\fontfamily{BebasNeue}\selectfont\huge \partname\nobreakspace\thepart
\par
\vskip 20\p@
\fi
\fontfamily{BebasNeue}\selectfont\Huge \bfseries #2\par}%
\@endpart}
\makeatother
% modifications to fncychap style Bjarne
\ChNameVar{\raggedleft\normalsize\fontfamily{BebasNeue}\selectfont}
\ChNumVar{\raggedleft\normalsize\fontfamily{BebasNeue}\selectfont}
\ChTitleVar{\raggedleft\huge\fontfamily{BebasNeue}\selectfont}
\makeatletter
\renewcommand\DOCH{%
\mghrulefill{\RW}\par\nobreak
\CNV\FmN{\@chapapp}\space \CNoV\thechapter\par\nobreak
\vskip -1\baselineskip\vskip 5pt
\mghrulefill{\RW}\par\nobreak
\vskip 20\p@
}
\makeatother
titlesecpackage works for those. – Andrew Swann Jan 02 '13 at 11:30\ChNameVaretc. The first example "Sonny" shows how to switch various parts to sansserif; the other examples should also be useful. – Andrew Swann Jan 03 '13 at 09:58