code: def filter(self, value):
          
          self._filter_input = value
          if value is None:
              self._filter = None
              self._filter_key = None
          else:
              new_filter = value.split(':')
              if len(new_filter) == 1:
                  self._filter = new_filter[0]
                  self._filter_key = None
              else:
                  self._filter = new_filter[1]
                  self._filter_key = new_filter[0]
  
          self._filter_re = None
          if self.filter is not None:
              logger.info("Set filter to {} on key {}".format(self.filter, self.filter_key))
              # Compute the regular expression
              try:
                  self._filter_re = re.compile(self.filter)
                  logger.debug("Filter regex compilation OK: {}".format(self.filter))
              except Exception as e:
                  logger.error("Cannot compile filter regex: {} ({})".format(self.filter, e))
                  self._filter = None
                  self._filter_re = None
                  self._filter_key = None
docs: Set the filter (as a sting) and compute the regular expression
          A filter could be one of the following:
          - python > Process name of cmd start with python
          - .*python.* > Process name of cmd contain python
          - username:nicolargo > Process of nicolargo user