title: How to perform os.environ join in python?
body: <p>I have a configuration of <code>os.environ</code> with default values (that cover 90% of my needs). I have a special application-framework-package, for example called <code>SALOME</code>, that does not provide package installation into system environment and tries to be self contained, it also requires use of special old technologies that rely on environmental variables thus  <code>sys.path</code> and <code>PYTHONPATH</code> are not the only things it needs. I can get all variables it needs when it started calling <code>os.environ</code> inside an environment it creates. I can then serialize that <code>os.environ</code> dictionary.</p>
  
  <p>I wonder how to apply a merge of <code>os.environ</code> I have on my currently running system with one I obtained by serializing?</p>