Currently, memoryview values can be assigned from all bytes-like objects (https://docs.python.org/3/glossary.html#term-bytes-like-object) except byte array.array:

----
import array

mview = memoryview(bytearray(b'hello'))

mview[:] = bytes(b'hello')  # success
mview[:] = bytearray(b'hello')  # success
mview[:] = memoryview(b'hello')  # success
mview[:] = array.array('b', b'hello')  # fail
----
    mview[:] = array.array('b', b'hello')
ValueError: memoryview assignment: lvalue and rvalue have different structures
----

>>> mview.format
'B'
>>> mview[:] = array.array('B', b'hello')


Bytes have format 'B', so this works as expected.