split byte string into lines

There is no reason to convert to string. Just give split bytes parameters. Split strings with strings, bytes with bytes.

>>> a = b'asdf\nasdf'
>>> a.split(b'\n')
[b'asdf', b'asdf']

Decode the bytes into unicode (str) and then use str.split:

Python 3.2.3 (default, Oct 19 2012, 19:53:16) 
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> a = b'asdf\nasdf'
>>> a.split('\n')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Type str doesn't support the buffer API
>>> a = a.decode()
>>> a.split('\n')
['asdf', 'asdf']
>>> 

You can also split by b'\n', but I guess you have to work with strings not bytes anyway. So convert all your input data to str as soon as possible and work only with unicode in your code and convert it to bytes when needed for output as late as possible.

try this.. .

rest = b"some\nlines"
rest=rest.decode("utf-8")

then you can do rest.split("\n")