Cannot Split, A bytes-like object is required, not 'str'

Use decode() correctly: either in two steps (if you want to reuse blah):

blah = blah.decode()
splitblah = blah.split("\n")
# other code that uses blah

or inline (if you need it for single use):

splitblah = blah.decode().split("\n")

Your issue with using decode() was that you did not use its return value. Note that decode() does not change the object (blah) to assign or pass it to something:

# WRONG!
blah.decode()

SEE ALSO:
decode docs.

If your question boils down to this:

I've tried using decode and encode but it still yells at me that the split method cannot use the datatype.

The error at hand can be demonstrated by the following code:

>>> blah = b'hello world'  # the "bytes" produced by check_output
>>> blah.split('\n')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: a bytes-like object is required, not 'str'

In order to split bytes, a bytes object must also be provided. The fix is simply:

>>> blah.split(b'\n')
[b'hello world']