create single bytes instance from sequence of memoryview

tl;dr Given a Sequence of memoryview, how can I create a single bytes instance without creating intermediate bytes instances?

The naive approach creates many intermediary instances of bytes

def create_bytes(seq_mv: Sequence[memoryview]) -> bytes:
    data = bytes()
    for mv in seq_mv:
        data = data + bytes(mv)
    return data

The function create_bytes creates len(seq_mv) + 1 instances of bytes during execution. That is inefficient.
I want create_bytes to create one new bytes instance during execution.

bytes as you got it, is an imutable object.

As the Tim Peters put in the comments, you can let Python create a single instance with all parts joined together with a single call to bytes().join(seq_mv).

If you need to perform any other operation on your data that would involve changing it in the way, you could be using the mutable bytearray instead- which not only gives you flexibility to change your object, but have all the advantages of mutable sequences.

You can then make a single conversion to bytes at the end of your function if the users of your function can't deal straight with a a bytearray (but maybe you can just return it directly):

def create_bytes(seq_mv: Sequence[memoryview]) -> bytes:
    data = bytearray()
    for mv in seq_mv:
        data.extend(mv)
    return bytes(data)

Or simply:

from functools import reduce

data = reduce(lambda data, mv: data.extend(mv), seq_mv, bytearray())