Add `.take_bytes([n])` a zero-copy path from `bytearray` to `bytes`

[cmaloney]

Feature or enhancement

Proposal:

Update bytearray to have its internal buffer always be a PyBytesObject and add a new method, .take_bytes([n]) which extracts that buffer.

.take_byes([n]) adds a way to go from a "mutable" buffer of bytes to an immutable one without requiring a memcpy.

This creates a path to resolve gh-60107

When would I use this?

Any code which makes a ba = bytearray(), modifies it, then calls bytes(ba). Other common patterns are bytes(ba); ba.clear() or bytes(ba[:n]); del ba[:n]. Note that if you want to discard data past a point, the most efficient pattern becomes ba.resize(n); ba.take_bytes() so that take_bytes([n]) doesn’t need to keep around the soon to be discarded extra bytes.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/add-take-bytes-n-to-bytearray-providing-a-zero-copy-path-to-bytes/103804/5

Linked PRs

• gh-139871: Add bytearray.take_bytes([n]) to efficiently extract bytes #140128