code: def select_bucket_region(custom_bucket, hook_region, stacker_bucket_region,
                           provider_region):
      
      region = None
      if custom_bucket:
          region = hook_region
      else:
          region = stacker_bucket_region
      return region or provider_region
docs: Returns the appropriate region to use when uploading functions.
  
      Select the appropriate region for the bucket where lambdas are uploaded in.
  
      Args:
          custom_bucket (str, None): The custom bucket name provided by the
              `bucket` kwarg of the aws_lambda hook, if provided.
          hook_region (str): The contents of the `bucket_region` argument to
              the hook.
          stacker_bucket_region (str): The contents of the
              `stacker_bucket_region` global setting.
          provider_region (str): The region being used by the provider.
  
      Returns:
          str: The appropriate region string.