def _get_env(environment, name):
    value = environment.get(name, _undefined)
    if isinstance(value, Undefined):
        raise UndefinedEnvironmentName('{0!r} does not exist in evaluation environment.'.format(name))
    return value
def _get_env(environment, name):
    value = environment.get(name, _undefined)
    if isinstance(value, Undefined):
        raise UndefinedEnvironmentName('{0!r} does not exist in evaluation environment.'.format(name))
    return value