code: def _get_partial_string_timestamp_match_key(self, key, labels):
          
          if isinstance(labels, MultiIndex):
              if (isinstance(key, str) and labels.levels[0].is_all_dates):
                  # Convert key '2016-01-01' to
                  # ('2016-01-01'[, slice(None, None, None)]+)
                  key = tuple([key] + [slice(None)] * (len(labels.levels) - 1))
  
              if isinstance(key, tuple):
                  # Convert (..., '2016-01-01', ...) in tuple to
                  # (..., slice('2016-01-01', '2016-01-01', None), ...)
                  new_key = []
                  for i, component in enumerate(key):
                      if (isinstance(component, str) and
                              labels.levels[i].is_all_dates):
                          new_key.append(slice(component, component, None))
                      else:
                          new_key.append(component)
                  key = tuple(new_key)
  
          return key
docs: Translate any partial string timestamp matches in key, returning the
          new key (GH 10331)