python.rb

#/usr/local/Homebrew/Library/Homebrew/language/python.rb  <-- this trait is located here
# Mixin module for {Formula} adding virtualenv support features.
    module Virtualenv
      def self.included(base)
        base.class_eval do
          resource "homebrew-virtualenv" do
            url PYTHON_VIRTUALENV_URL
            sha256 PYTHON_VIRTUALENV_SHA256
          end
        end
      end
      .
      .
      .