def render(self, context):
    field = template.resolve_variable(self.field_var, context)
    # Caling bound_field.as_widget() returns the HTML, but we need to 
    # intercept this to manipulate the attributes - so we have to 
    # duplicate the logic from as_widget here.
    widget = field.field.widget
    attrs = self.extra_attrs or {}
    attrs = attrs.copy() # <--------------------------- HERE
    auto_id = field.auto_id
    if auto_id and 'id' not in attrs and 'id' not in widget.attrs:
        attrs['id'] = auto_id
    if not field.form.is_bound:
        data = field.form.initial.get(field.name, field.field.initial)
        if callable(data):
            data = data()
    else:
        data = field.data
    html = widget.render(field.html_name, data, attrs=attrs)
    # Finally, if we're NOT in xhtml mode ensure no '/>'
    doctype = getattr(context, '_doctype', 'xhtml1')
    if doctype in html_doctypes:
        html = xhtml_end_re.sub('>', html)

    return html