code: def __init__(self):
      try:
          self.cache_location = os.environ[LOCATION_ENVVAR]
      except KeyError:
          raise WorkflowError(
              "Output file cache activated (--cache), but no cache "
              "location specified. Please set the environment variable "
              "${}.".format(LOCATION_ENVVAR)
          )
      self.provenance_hash_map = ProvenanceHashMap()
  
file_path: snakemake/snakemake/caching/__init__.py
imports: from abc import ABCMeta, abstractmethod
  import os
  from snakemake.jobs import Job
  from snakemake.io import apply_wildcards
  from snakemake.exceptions import WorkflowError, CacheMissException
  from snakemake.caching.hash import ProvenanceHashMap
label_desc: Use image node_id 1 to create a new AbstractOutputFileCache object  with example: obj = AbstractOutputFileCache()