how to get bytes from bytearray without copying

[Juraj Ivančić]

Is it possible to somehow 'steal' bytearray's buffer and make it a 
read-only bytes? I failed to find a way to do this, and would like to 
make sure.

My use case is, I would expect, fairly common. I read a certain 
(potentially very large) amount of data from the network into a 
pre-allocated bytearray. From that point on, this data is logically 
read-only. To prevent making redundant copies, I wrap it in a 
memoryview, and then slice and dice it. The problem with this memoryview 
is that it, and its slices, are considered writable, and thus cannot be 
hashed:

ValueError: cannot hash writable memoryview object

The only way (AFAICT) to make this work is to first create a bytes 
object from bytearray, but this copies the data. I don't need this copy, 
so I'd like to avoid it, because of both principle and performance reasons.

Is there any reason why bytearray isn't able to release/convert its 
buffer to bytes? I see that it has a clear() method which... well... 
clears it. The former would be much more useful.

I would also be content if there is some way of making memoryview 
artificially read-only to avoid the above error.

Any help/thoughts/comments are highly appreciated.