code: def field_(self, name):
      
      try:
          field = self.fields[name]
      except KeyError:
          raise KeyError("Key %r not found in '%s'" % (name, self.__class__.__name__))
      return BoundField(self, field, name)
docs: From https://github.com/halfnibble/django-underscore-filters
  
      Get a form field starting with _.
      Taken near directly from Django > forms.
      Returns a BoundField with the given name.