Tiny perf nitpick, you shouldn't use a dictionary here as you are not going to query it by the keys.

It should be a list of tuples:
```python
BSD_TCP_METRICS = [
      (re.compile("^\s*(\d+) data packets \(\d+ bytes\) retransmitted\s*$"), 'system.net.tcp.retrans_packs'),
      (re.compile("^\s*(\d+) packets sent\s*$"), 'system.net.tcp.sent_packs'),
      (re.compile("^\s*(\d+) packets received\s*$"), 'system.net.tcp.rcv_packs'),
]
```
and then you'll be able to iterate with:
```python
for regex, metric_name in BSD_TCP_METRICS:
```