tomoStream python server crashes if tomoScan IOC is not running

[decarlof]

with error:

Traceback (most recent call last):
  File "start_tomostream.py", line 6, in <module>
    ts = TomoStream(["../../db/tomoStream_settings.req","../../db/tomoStream_settings.req"], {"$(P)":"2bmb:", "$(R)":"TomoStream:"})
  File "/local/tomo/conda/anaconda/envs/streaming/lib/python3.7/site-packages/tomostream-0.1-py3.7.egg/tomostream/tomostream.py", line 52, in __init__
    self.epics_pvs['ThetaArray']         = PV(self.epics_pvs['PSOPVPrefix'].get(as_string=True) + 'motorPos.AVAL')
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

[decarlof]

adding here:

if self.epics_pvs['PSOPVPrefix'].get(as_string=True) == None:
        log.error("TomoScan is down. Please start TomoScan first")
        exit() # this is ignored when starting this with pythion -i
        

does not work = the error message is printed but the script keeps running in the interactive mode and I still get the error:

Traceback (most recent call last):
  File "start_tomostream.py", line 6, in <module>
    ts = TomoStream(["../../db/tomoStream_settings.req","../../db/tomoStream_settings.req"], {"$(P)":"2bmb:", "$(R)":"TomoStream:"})
  File "/local/tomo/conda/anaconda/envs/streaming/lib/python3.7/site-packages/tomostream-0.1-py3.7.egg/tomostream/tomostream.py", line 52, in __init__
    self.epics_pvs['ThetaArray']         = PV(self.epics_pvs['PSOPVPrefix'].get(as_string=True) + 'motorPos.AVAL')
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

[decarlof]

@nikitinvv how about

if self.epics_pvs['PSOPVPrefix'].get(as_string=True) == None:
        log.error("TomoScan is down")
        log.error("Type exit() here and start TomoScan first")
        return
        

this way

python -i start_tomostream.py
2021-01-11 18:17:07,693 - TomoScan is down
2021-01-11 18:17:07,693 - Type exit() here and start TomoScan first
>>>

In other words I avoid the TypeError message, I print a red error log message, the python tomostream server is not set but its iterative session is still up and needs to be restarted