code: def call_s3guard_prune(credential_name):
      # Get the AWS credential account associated with the credential
    account = get_external_account(api, credential_name)
    # Invoke the prune command for the account by its name
    cmd = account.external_account_cmd_by_name('S3GuardPrune')
    print ("Issued '{0}' command with id '{1}'".format(cmd.name, cmd.id))
    print ("Waiting for command {0} to finish...".format(cmd.id))
    cmd = cmd.wait()
    print ("Command succeeded: {0}".format(cmd.success))
docs: Runs S3Guard prune command on external account associated with the
    given credential_name.