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>>> lst = [0x0A, 0x0B, 0x0C, 'string']
>>> 
>>> bt = bytearray()
>>> for i in lst:
...     if type(i) is int:
...         bt.append(i)
...     else:
...         bt.extend(i.encode('latin1'))
... 
>>> bt
bytearray(b'\n\x0b\x0cstring')
>>>

# python 2.x
for i in lst:
    if isinstance(i, (int, long)):
        bt.append(chr(i))
...
# python 3.x
for i in lst:
    if isinstance(i, int):
        bt.append(i.to_bytes(1, byteorder='big'))
...

>>> (256).to_bytes(1, 'big')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: int too big to convert
>>>

>>> (256).to_bytes(4, 'big')
b'\x00\x00\x01\x00'
>>>

>>> (256).to_bytes(2, 'big')
b'\x01\x00'
>>> '\x01\x00'.encode('latin1')
b'\x01\x00'
>>>