pyhf json2xml requires parameter inits

[alexander-held]

Summary

When converting a workspace via pyhf json2xml, the model config seems to rely on the presence of parameter inits, even though the spec does not strictly require them.

OS / Environment

n/a

Steps to Reproduce

workspace:

{
    "channels": [
        {
            "name": "ch",
            "samples": [
                {
                    "data": [1000.0],
                    "modifiers": [
                        {"data": null, "name": "mu_sig", "type": "normfactor"},
                        {
                            "data": {"hi": 1.5, "lo": 0.5},
                            "name": "unc",
                            "type": "normsys"
                        }
                    ],
                    "name": "signal"
                }
            ]
        }
    ],
    "measurements": [
        {
            "config": {
                "parameters": [
                    {
                        "name": "mu_sig",
                        "bounds": [[0, 10]]
                    }
                ],
                "poi": "mu_sig"
            },
            "name": "meas"
        }
    ],
    "observations": [{"data": [1000], "name": "ch"}],
    "version": "1.0.0"
}

convert with pyhf json2xml:

...
  File "[...]/pyhf/src/pyhf/cli/rootio.py", line 88, in json2xml
    writexml.writexml(
  File "[...]/pyhf/src/pyhf/writexml.py", line 292, in writexml
    channel = build_channel(spec, channelspec, spec.get('observations'))
  File "[...]/pyhf/src/pyhf/writexml.py", line 271, in build_channel
    channel.append(build_sample(spec, samplespec, channelspec['name']))
  File "[...]/pyhf/src/pyhf/writexml.py", line 245, in build_sample
    modifier = build_modifier(
  File "[...]/pyhf/src/pyhf/writexml.py", line 181, in build_modifier
    val = p['inits'][0]
KeyError: 'inits'

A fit with pyhf fit works perfectly fine. The addition of "inits": [1.0] in the model config also fixes the crash, as does removing this parameter configuration completely.

File Upload (optional)

No response

Expected Results

I expect the conversion to not rely on the presence of inits. The default of 1.0 may not make sense if some custom bounds are specified, but I think this is on the user to fix. The same issue also appears when just setting a normfactor to constant without specifying the inits.

Actual Results

File "[...]/pyhf/src/pyhf/cli/rootio.py", line 88, in json2xml
    writexml.writexml(
  File "[...]/pyhf/src/pyhf/writexml.py", line 292, in writexml
    channel = build_channel(spec, channelspec, spec.get('observations'))
  File "[...]/pyhf/src/pyhf/writexml.py", line 271, in build_channel
    channel.append(build_sample(spec, samplespec, channelspec['name']))
  File "[...]/pyhf/src/pyhf/writexml.py", line 245, in build_sample
    modifier = build_modifier(
  File "[...]/pyhf/src/pyhf/writexml.py", line 181, in build_modifier
    val = p['inits'][0]
KeyError: 'inits'

pyhf Version

0.6.3

Code of Conduct

• I agree to follow the Code of Conduct

[matthewfeickert]

Thanks for raising this @alexander-held. 👍