How do you put a period after the section number using the article class?

Question

I am using the article class with the code:

\documentclass[12pt]{article}

\begin{document}
\section{Foo}
This is an example of foo.
\section{Bar}
This is an example of bar.
\end{document}

This produces:

1 Foo

2 Bar

What I want is a period after the section number:

1. Foo

2. Bar

I cannot change away from the article class. How would I accomplish this?

Answer 1

Use the titlesec package and put in the preamble:

\titlelabel{\thetitle.\quad}

Answer 2

\renewcommand{\thesection}{\arabic{section}.}