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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _construct_context_for_args(args):
 """Construct a new Context for the parsed arguments. Args: args: the dictionary of magic arguments. Returns: A new Context based on the current default context, but with any explicitly specified arguments overriding the default's config. """

  global_default_context = google.datalab.Context.default()
  config = {}
  for key in global_default_context.config:
    config[key] = global_default_context.config[key]

  billing_tier_arg = args.get('billing', None)
  if billing_tier_arg:
    config['bigquery_billing_tier'] = billing_tier_arg

  return google.datalab.Context(
    project_id=global_default_context.project_id,
    credentials=global_default_context.credentials,
    config=config)