code: def _reducedProtToPeps(protToPeps, proteins):
      
      return {k: v for k, v in viewitems(protToPeps) if k not in proteins}
docs: Returns a new, reduced "protToPeps" dictionary that does not contain
      entries present in "proteins".
  
      :param protToPeps: dict, for each protein (=key) contains a set of
          associated peptides (=value). For Example {protein: {peptide, ...}, ...}
      :param proteins: a list of proteinSet
      :returns: dict, protToPeps not containing entries from "proteins"