Python django.forms.widgets 模块，Input() 实例源码

def render_layout(self, form, context, template_pack=TEMPLATE_PACK):
        """
        Copy any field label to the ``placeholder`` attribute.
        Note, this method is called when :attr:`layout` is defined.
        """
        # Writing the label values into the field placeholders.
        # This is done at rendering time, so the Form.__init__() could update any labels before.
        # Django 1.11 no longer lets EmailInput or URLInput inherit from TextInput,
        # so checking for `Input` instead while excluding `HiddenInput`.
        for field in form.fields.values():
            if field.label and \
                    isinstance(field.widget, (Input, forms.Textarea)) and \
                    not isinstance(field.widget, forms.HiddenInput):
                field.widget.attrs['placeholder'] = u"{0}:".format(field.label)

        return super(CompactLabelsCommentFormHelper, self).render_layout(form, context, template_pack=template_pack)