Use repr for an Attribute value

[KommuSoft]

For string values for attributes, for example on a GenericAPIView, it uses:

lookup_field = pk

(see https://www.cdrf.co/3.7/rest_framework.generics/GenericAPIView.html )

It thus fails to perform a repr over the item and thus displays it as a variable. We can use repr to show this as:

lookup_field = 'pk'

instead.