Render MAC addresses with bytes.hex(":")

CHANGELOG.md

@@ -7,6 +7,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+- `bytes_to_mac` renders addresses with `bytes.hex(":")` instead of a
+ generator over `format()`. The old form ran seven generator steps and
+ six `format()` calls per address, twice per Ethernet frame, and showed
+ up in a corpus profile as 88,200 generator calls. Measured 16–29×
+ faster on the call depending on run. Output is byte-for-byte
+ identical, and `memoryview.hex` takes a separator too, so a
+ decode-time view still works. No API change.
+
 ### Fixed
 - **The release workflow can no longer publish untested code.** Pushing
  a `v*` tag ran `uv build` and `uv publish` with no dependency on the

src/netprotocols/_base.py

@@ -47,7 +47,11 @@ def mac_to_bytes(mac: str) -> bytes:
 
 def bytes_to_mac(data: bytes) -> str:
  """Render 6 raw bytes as a colon-separated lowercase MAC address."""
- return ":".join(format(octet, "02x") for octet in data)
+ # bytes.hex(sep) does this in one C call; the generator-plus-format
+ # equivalent it replaces ran seven generator steps and six format()
+ # calls per address, twice per Ethernet frame. memoryview.hex takes
+ # a separator too, so this still accepts a decode-time view.
+ return data.hex(":")
 
 
 def ipv4_to_bytes(addr: str) -> bytes: