code: def environment_does_base_variable_exist(self, name):
          
          if not isinstance(name, basestring):
              raise TypeError("name can only be an instance of type basestring")
          exists = self._call("environmentDoesBaseVariableExist",
                       in_p=[name])
          return exists
docs: Checks if the given environment variable exists in the session's base
          environment (:py:func:`IGuestSession.environment_base` ).
  
          in name of type str
              Name of the environment variable to look for.  This cannot be
              empty nor can it contain any equal signs.
  
          return exists of type bool
              TRUE if the variable exists, FALSE if not.
  
          raises :class:`VBoxErrorNotSupported`
              If the guest additions does not
  support the session base environment feature.  Support for this was
  introduced with protocol version XXXX.
          
          raises :class:`VBoxErrorInvalidObjectState`
              If the guest additions has
  yet to report the session base environment.