code: def p_expression_ID(p):
      
      lookup = compa2lookup[p[2]]
  
      try:
          field = get_shortcut(p[1])
      except KeyError:
          field = p[1]
  
      if lookup:
          field = '%s__%s' % (field, lookup)
  
      # In some situations (which ones?), python
      # refuses unicode strings as dict keys for
      # Q(**d)
      field = str(field)
  
      d = {field: p[3]}
  
      p[0] = Q(**d)
docs: expression : FIELD operation value