old_contents: import os
  import photomosaic.flickr
  import photomosaic as pm
  
  
  if not os.path.isfile(os.path.expanduser('~/pools/cats/pool.json')):
      FLICKR_API_KEY = os.environ['FLICKR_API_KEY']
      pm.set_options(flickr_api_key=FLICKR_API_KEY)
  
      photomosaic.flickr.from_search('cats', '~/pools/cats/')
      pool = pm.make_pool('~/pools/cats/*.jpg')
      pm.export_pool(pool, '~/pools/cats/pool.json')  # save color analysis for future reuse
  
new_contents: import os
  import photomosaic.flickr
  import photomosaic as pm
  
  
  class MissingAPIKey(Exception):
      ...
  
  
  if not os.path.isfile(os.path.expanduser('~/pools/cats/pool.json')):
      try:
          FLICKR_API_KEY = os.environ['FLICKR_API_KEY']
      except KeyError:
          raise MissingAPIKey(
              "This script requires the environment variable FLICKR_API_KEY "
              "to run. It will be not be available on pull requests from "
              "other forks. See "
              "https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions"
              ) from None
      pm.set_options(flickr_api_key=FLICKR_API_KEY)
  
      photomosaic.flickr.from_search('cats', '~/pools/cats/')
      pool = pm.make_pool('~/pools/cats/*.jpg')
      pm.export_pool(pool, '~/pools/cats/pool.json')  # save color analysis for future reuse
  else:
      print("Pool was found in ~pools/cats/. No action needed.")
  
subject: Improve error message if FLICKR_API_KEY is missing