My first Chef definition: create a virtualenv. Be nice.

virtualenv-example.rb

# An example of the below

virtualenv "/home/dvcsmirrors/hg" do
    owner "root"
    group "dvcsmirrors"
    mode 0775
    packages "Mercurial" => "1.6.3",
             "hgsubversion" => "1.1.2"
end

virtualenv.rb

#
# Definition to create virtualenvs
#
# For example::
#
#   virtualenv "/home/me/myenv" do
#       packages "Django" => "1.2.3"
#   end
#
# This would create a new virtualenv in /home/me/myenv and install
# Django 1.2.3. "packages" is a hash, so you can include multiple
# packages there. Right now there's nothing to say "latest version"
# because I don't know Ruby that well!
#
# The definition also accepts path, owner, group, and mode arguments, just
# like the directory resource.
#
# TODO: support a requirements file.
#

define :virtualenv, :action => :create, :owner => "root", :group => "root", :mode => 0755, :packages => {} do
    path = params[:path] ? params[:path] : params[:name]
    if params[:action] == :create
        # Manage the directory.
        directory path do
            owner params[:owner]
            group params[:group]
            mode params[:mode]
        end
        execute "create-virtualenv-#{path}" do
            command "virtualenv #{path}"
            not_if "test -f #{path}/bin/python"
        end
        params[:packages].each_pair do |package, version|
            pip = "#{path}/bin/pip"
            execute "install-#{package}-#{path}" do
                command "#{pip} install #{package}==#{version}"
                not_if "[ `#{pip} freeze | grep #{package} | cut -d'=' -f3` = '#{version}' ]"
            end
        end
    elsif params[:action] == :delete
        directory path do
            action :delete
            recursive true
        end
    end
end

Helpful, thanks!