code: def get_var(self, name, user=None):
          
          # Retrieve a user variable
          if user is not None:
              if user not in self._users:
                  raise UserNotDefinedError
  
              return self._users[user].get_var(name)
  
          # Retrieve a global variable
          if name not in self._global_vars:
              raise VarNotDefinedError
  
          return self._global_vars[name]
docs: Retrieve a global or user variable
          :param name: The name of the variable to retrieve
          :type  name: str
  
          :param user: If retrieving a user variable, the user identifier
          :type  user: str or None
  
          :rtype: str
  
          :raises UserNotDefinedError: The specified user does not exist
          :raises VarNotDefinedError: The requested variable has not been defined