This script lives in /reg/g/psdm/tutorials/examplePython/randomAccess.py and demonstrates how to jump to a specific event using the three "timestamp" numbers that uniquely identify an LCLS event: seconds/nanoseconds/fiducials (fiducials increment at 360Hz and repeat every ~20 minutes, the other two numbers are a standard unix seconds/nanoseconds timestamp). In LCLS-II there will be only one number that will identify an event.
from psana import *
ds = DataSource('exp=xpptut15:run=54:smd')
# LCLS uses 3 numbers to define an event. In LCLS2 this will be one number.
seconds = []
nanoseconds = []
fiducials = []
# get some times of events (these could come from a saved "small data" file, for example)
for nevent,evt in enumerate(ds.events()):
evtId = evt.get(EventId)
seconds.append(evtId.time()[0])
nanoseconds.append(evtId.time()[1])
fiducials.append(evtId.fiducials())
if nevent==2: break
# now that we have the times, jump to the events in reverse order
ds = DataSource('exp=xpptut15:run=54:idx')
run = ds.runs().next()
for sec,nsec,fid in zip(reversed(seconds),reversed(nanoseconds),reversed(fiducials)):
et = EventTime(int((sec<<32)|nsec),fid)
evt = run.event(et)
print evt.get(EventId).fiducials()
This example shows how one uses "idx" (or "index") mode to iterate over events randomly:
from psana import *
ds = DataSource('exp=xpptut15:run=54:idx')
run = ds.runs().next()
times = run.times()
print 'Found',len(times),'events in run'
for nevt,t in enumerate(times):
evt = run.event(t)
if nevt==2: break
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