One way to check that it's bytes-compatible is to take a memoryview of it:
>>> memoryview(b"abc")
<memory at 0x1cf5120>
>>> memoryview(bytearray(b"abc"))
<memory at 0x1cf55a0>
>>> memoryview(array.array('b', b"abc"))
<memory at 0x1cf52a0>
>>> memoryview([b"abc"])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: cannot make memory view because object does not have the buffer interface
>>> memoryview("abc")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: cannot make memory view because object does not have the buffer interface