编码解码和bytearray转换错误

Question

我试图理解为什么2和5命令会引发错误：

1 >>> s = 'it�s'

2 >>> s.encode('utf-8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2: ordinal not in range(128)

3 >>> print s.decode('utf-8').encode('utf-8')
it�s

4 >>> bytearray(s.decode('utf-8').encode('utf-8'))
bytearray(b'it\xc3\xaf\xc2\xbf\xc2\xbds')

5 >>> bytearray(s.decode('utf-8').encode('utf-8', 'ignore'), 'utf-8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2: ordinal not in range(128)

我认为s.decode('utf-8','ignore').encode('utf-8')正在将s转换为utf-8而忽略了奇怪的事情。那么，为什么在bytearray中转换为utf-8编码会引发错误？