class_docstr: Expansions.
  Replaces each contraction with its expanded version.
  
  Perturbation example:
  
  **Input:**
      She's a doctor, and I'm a student
  
  **Output:**
      She is a doctor, and I am a student
code: def perturb(self, text: str, rng: Random) -> str:
      def expand_match(contraction):
          match = contraction.group(0)
          expanded_contraction = self.contraction_map.get(
              match, self.contraction_map.get(match.lower())
          )
          return match_case(match, expanded_contraction)
  
      return self.contraction_pattern.sub(expand_match, text)
  
file_path: H2O/h2o_hf/helm/src/helm/benchmark/augmentations/contraction_expansion_perturbation.py
imports: from typing import Dict
  import re
  from random import Random
  from helm.common.general import match_case
  from .perturbation import Perturbation
  from .perturbation_description import PerturbationDescription
label_desc: Use image node_id 3 for calling the ExpansionPerturbation obj's underlying member method code with example usage: obj.perturb(text, rng) and returns: self, match_case