docs: def _warn_dupkey(self, k):
          """
          Really odd function - used to help ensure we actually warn for duplicate
          keys.
          """
          if self._privflags & PYCBC_CONN_F_WARNEXPLICIT:
              warnings.warn_explicit(
                  'Found duplicate keys! {0}'.format(k), RuntimeWarning,
                  __file__, -1, module='couchbase_ffi.bucket', registry={})
          else:
              warnings.warn('Found duplicate keys!', RuntimeWarning)