docs: def fileset(self, name, from_study=None, format=None):  # @ReservedAssignment @IgnorePep8
          """
          Gets the fileset named 'name' produced by the Study named 'study' if
          provided. If a spec is passed instead of a str to the name argument,
          then the study will be set from the spec iff it is derived
  
          Parameters
          ----------
          name : str | FilesetSpec
              The name of the fileset or a spec matching the given name
          from_study : str | None
              Name of the study that produced the fileset if derived. If None
              and a spec is passed instaed of string to the name argument then
              the study name will be taken from the spec instead.
          format : FileFormat | str | None
              Either the format of the fileset to return or the name of the
              format. If None and only a single fileset is found for the given
              name and study then that is returned otherwise an exception is
              raised
          """
          if isinstance(name, BaseFileset):
              if from_study is None and name.derived:
                  from_study = name.study.name
              name = name.name
          try:
              format_dct = self._filesets[(name, from_study)]
          except KeyError:
              available = [
                  ('{}(format={})'.format(f.name, f._resource_name)
                   if f._resource_name is not None else f.name)
                  for f in self.filesets if f.from_study == from_study]
              other_studies = [
                  (f.from_study if f.from_study is not None else '<root>')
                  for f in self.filesets if f.name == name]
              if other_studies:
                  msg = (". NB: matching fileset(s) found for '{}' study(ies) "
                         "('{}')".format(name, "', '".join(other_studies)))
              else:
                  msg = ''
              raise ArcanaNameError(
                  name,
                  ("{} doesn't have a fileset named '{}'{} "
                     "(available '{}'){}"
                     .format(self, name,
                             (" from study '{}'".format(from_study)
                              if from_study is not None else ''),
                             "', '".join(available), msg)))
          else:
              if format is None:
                  all_formats = list(format_dct.values())
                  if len(all_formats) > 1:
                      raise ArcanaNameError(
                          "Multiple filesets found for '{}'{} in {} with formats"
                          " {}. Need to specify a format"
                          .format(name, ("in '{}'".format(from_study)
                                         if from_study is not None else ''),
                                  self, "', '".join(format_dct.keys())))
                  fileset = all_formats[0]
              else:
                  try:
                      if isinstance(format, str):
                          fileset = format_dct[format]
                      else:
                          try:
                              fileset = format_dct[format.ext]
                          except KeyError:
                              fileset = None
                              for rname, rfileset in format_dct.items():
                                  if rname in format.resource_names(
                                          self.tree.repository.type):
                                      fileset = rfileset
                                      break
                              if fileset is None:
                                  raise
                  except KeyError:
                      raise ArcanaNameError(
                          format,
                          ("{} doesn't have a fileset named '{}'{} with "
                           "format '{}' (available '{}'){}"
                             .format(self, name,
                                     (" from study '{}'".format(from_study)
                                      if from_study is not None else ''),
                                     format,
                                     "', '".join(format_dct.keys()), msg)))
  
          return fileset