Added check for response function

[s-schneider]

What does this PR do?

Adds write support for AH (Ad Hoc) format to stream.write(), It is an addition to PR #1757

Why was it initiated? Any relevant Issues?

related to issue #1754

PR Checklist

• This PR is not directly related to an existing issue (which has no PR yet).
• All tests still pass.
• Any new features or fixed regressions are be covered via new tests.
• Any new or changed features have are fully documented.
• Significant changes have been added to CHANGELOG.txt .
• First time contributors have added your name to CONTRIBUTORS.txt .

[megies]

In general we nowadays don't encourage "magic uses" of additional items in Trace.stats anymore.. but if it's important for you we might still accept this change I guess..

[s-schneider]

Would there be a better way to check if there is a response attached?

[krischer]

I'd personally either like to see this as tr.stats.ah.response or Stream.write(..., format="AH", response=response). Adding important things to tr.stats is a hack in any case and we should not keep doing this - there are already enough places in our code base that do that.

[s-schneider]

I use the information provided for instance by the get_waveforms(attach_response=True) of obspy.clients.fdsn. I didn't add that information manually.

[krischer]

Yea- this is one of the instances in our code base where it does already happen. I'd be fine with a construct like this which offers a cleaner interface but also falls back to using the existing tr.stats.response:

def _write_ah(..., response=None, ...):
    ...
    # First use passed response, otherwise look in trace.stats.
    if response is None and "response" in tr.stats:
        response = tr.stats.response

    if response:
        ...