class_docstr: Also immutable.
class_docstr_tok: ["Also","immutable","."]
code: def __init__(self, efactors):
      self.efactors = frozenset(efactors)
  
imports: from __future__ import print_function
  from patsy.util import no_pickling
label_desc: Use image node_id 1 to create a new _Subterm object from inherited base classes: object with example: obj = _Subterm(efactors)