# Todo 1
log = print

def ensure(condition, message):
    if condition:
        log('*** 测试成功')
    else:
        log('*** 测试失败:', message)
        
        
def n_char(n, fill_char='0'):
    return fill_char * n
def zfill(n, width):
    s = str(n)
    length = len(s)
    if length < width:
        n = width - length
        r = n_char(n) + s
        return r
    else:
        return s


def test_zfill():
    ensure(zfill(1, 4) == '0001', 'zfill 测试 1')
    ensure(zfill(23, 4) == '0023', 'zfill 测试 2')
    ensure(zfill(12345, 4) == '12345', 'zfill 测试 3')
    ensure(zfill(169, 5) == '00169', 'zfill 测试 4')

test_zfill()