Unable to fit with load_multi_arf/load_multi_rmf: startup() takes 1 positional argument but 2 were given

[DougBurke]

Summary

Noted by SDS, Sherpa 4.12 (CIAO 4.12) has the following error:

sherpa In [1]: load_pha(1, "460_leg_m1_bin10.pha")                                                                                                               
WARNING: systematic errors were not found in file '460_leg_m1_bin10.pha'
statistical errors were found in file '460_leg_m1_bin10.pha' 
but not used; to use them, re-read with use_errors=True
read background_up into a dataset from file 460_leg_m1_bin10.pha
read background_down into a dataset from file 460_leg_m1_bin10.pha

sherpa In [2]: load_multi_arfs(1, ["460_LEG_-1.garf","460_LEG_-2.garf","460_LEG_-3.garf"], [1,2,3]) 

sherpa In [3]: load_multi_rmfs(1, ["460_leg_-1.grmf","460_leg_-2.grmf","460_leg_-3.grmf"], [1,2,3]) 

sherpa In [4]: mdl = xswabs.abs1 * xsbknpower.bpow1 

sherpa In [5]: set_model(1, mdl)                                                                                            

sherpa In [6]: bpow1.norm = 0.05                                                                                            

sherpa In [7]: plot_fit(ylog=True)                                                                                          

The plot works - i.e. you can evaluate the model - but when you come to try to fit it (the sys.tracebacklimit setting is to make sure we get a reasonable traceback here) the fit fails

sherpa In [8]: import sys                                                                                                   

sherpa In [9]: sys.tracebacklimit = 1                                                                                       

sherpa In [10]: fit()                                                                                                       
WARNING: data set 1 has associated backgrounds, but they have not been subtracted, nor have background models been set
  File "/home/dburke/anaconda3/envs/ciao412/lib/python3.7/site-packages/IPython/core/interactiveshell.py", line 3319, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
TypeError: startup() takes 1 positional argument but 2 were given

Workaround

This can be worked around by monkey-patching the startup method of the problematic class before any instances have been created:

# patch the startup method of the MultiResponseSumModel *before* any
# instances have been created
#
import numpy
from sherpa.models.model import CompositeModel
from sherpa.astro.instrument import MultiResponseSumModel

def startup_monkey(self, cache):
    pha = self.pha
    if numpy.iterable(pha.mask):
        pha.notice_response(True)
    self.channel = pha.get_noticed_channels()
    self.mask = pha.get_mask()
    self._get_noticed_energy_list()
    CompositeModel.startup(self, cache)

MultiResponseSumModel.startup = startup_monkey

If you have this in a file (e.g. patchit.py) then you can

sherpa In [1]: %run -i patchit.py

and then you can fit data with multiple ARF/RMF

Details

This is similar to the issue that lead to #701 - a startup method needs to know about the cache argument. Should we make the default cache routine have *args / **kwargs so that this doesn't happen (there are plenty of other startup methods in classes which take no arguments)?

The fix for this particular case is easy, but we have no tests for load_multi_arfs / load_multi_rmfs which is going to take longer to put together.

[DougBurke]

Closing as fixed in #728