code: def freeze(environ, names, label=None):
      
      diff = _get_diff(environ, label)
      for name in names:
          diff[name] = environ.get(name)
      environ[_variable_name(label)] = _dumps(diff)
docs: Flag the given names to reset to their current value in the next Python.
      
      :param dict environ: The environment that will be passed to the next Python.
      :param names: A list of variable names that should be reset to their current
          value (as in ``environ``) when the next sub-Python starts.
      :param str label: A name for this environment freeze; the default of ``None``
          will be unfrozen at startup.
      
      This is useful to reset environment variables that are set by wrapper
      scripts that are nessesary to bootstrap the process, but we do not want to
      carry into any subprocess. E.g. ``LD_LIBRARY_PATH``.
  
      This may be called multiple times for the same label as it updates any
      existing freezes.
      
      Usage::
      
          import os
          from subprocess import call
          
          from sitecustomize.environ import freeze
          
          env = dict(os.environ)
          env['DEMO'] = 'one'
          freeze(env, ['DEMO'])
          env['DEMO'] = 'two'
          
          call(['python', '-c', 'import os; print os.environ["DEMO"]'], env=env)
          # Prints: one