          request = self.context.get('request', None)
          format = self.context.get('format', None)
          view_name = self.view_name or self.parent.opts.view_name
          kwargs = {self.pk_url_kwarg: obj.pk}
          try:
              return reverse(view_name, kwargs=kwargs, request=request, format=format)
          except:
              pass
 
</s> remove         format = self.format or self.context.get('format', None)
 </s> add         format = self.context.get('format', None)
        # By default use whatever format is given for the current context
        # unless the target is a different type to the source.
        #
        # Eg. Consider a HyperlinkedIdentityField pointing from a json
        # representation to an html property of that representation...
        #
        # '/snippets/1/' should link to '/snippets/1/highlight/'
        # ...but...
        # '/snippets/1/.json' should link to '/snippets/1/highlight/.html'
        if format and self.format and self.format != format:
            format = self.format

          request = self.context.get('request', None)
          format = self.context.get('format', None)
          view_name = self.view_name or self.parent.opts.view_name
          kwargs = {self.pk_url_kwarg: obj.pk}
        # By default use whatever format is given for the current context
        # unless the target is a different type to the source.
        #
        # Eg. Consider a HyperlinkedIdentityField pointing from a json
        # representation to an html property of that representation...
        #
        # '/snippets/1/' should link to '/snippets/1/highlight/'
        # ...but...
        # '/snippets/1/.json' should link to '/snippets/1/highlight/.html'
        if format and self.format and self.format != format:
            format = self.format

          try:
              return reverse(view_name, kwargs=kwargs, request=request, format=format)
          except:
              pass
keep keep keep add keep keep keep keep
 Tweak behavior of hyperlinked fields that include an explicit format suffix. 
rest_framework/relations.py