documentclass{article}
usepackage[T1]{fontenc}
usepackage[lighttt]{lmodern} % bold and italic ttfamily
usepackage{color}
usepackage{listings}
usepackage{setspace}

definecolor{Code}{rgb}{0.1,0.1,0.1}
definecolor{Decorators}{rgb}{0.7,0,0.7}
definecolor{Numbers}{rgb}{0.5,0,0}
definecolor{MatchingBrackets}{rgb}{0.25,0.5,0.5}
definecolor{Keywords}{rgb}{0,0,1}
definecolor{self}{rgb}{.87,.46,0}
definecolor{Strings}{rgb}{0,0.66,0}
definecolor{Comments}{rgb}{0.388,0.4705,0.518}
definecolor{Backquotes}{rgb}{0,0,0}
definecolor{Classname}{rgb}{0,0,0}
definecolor{FunctionName}{rgb}{0,0,0}
definecolor{Operators}{rgb}{0,0,0}
definecolor{Background}{rgb}{0.99,0.99,0.99}

lstset{
language=Python,
numbers=left,
numberstyle=footnotesize,
numbersep=1em,
xleftmargin=3em,
linewidth=23cm,
framextopmargin=1em,
framexbottommargin=1em,
showspaces=false,
showtabs=false,
showstringspaces=false,
frame=l,
tabsize=4,
% Basic
basicstyle=ttfamilysmall,
backgroundcolor=color{Background},
% Comments
commentstyle=color{Comments}slshape,
% Strings
stringstyle=color{Strings},
morecomment=[s][color{Strings}]{"""}{"""},
morecomment=[s][color{Strings}]{'''}{'''},
% keywords
keywordstyle={color{Keywords}bfseries},
% additional keywords
keywordstyle={[2]color{Decorators}},
emph={self},
emphstyle={color{self}slshape},
}%




begin{document}
lstset{language=Python, breaklines=true}
begin{lstlisting}
    class MyClass:
        def __init__(self):
            print('do a thing')

    foo = MyClass()
end{lstlisting}

end{document}

lstset{moredelim=[s][bfseries]{class }{:},
    moredelim=[s][bfseries]{def }{(},}