Python scripting in IceTray

Generally IceTray is controlled via a python script which sets up the needed modules and services, executes the Tray and cleans things up. The best illustration of this is a simple example:

#!/usr/bin/env python
#
# Pass 2:

from I3Tray import *

from os.path import expandvars

import os
import sys

load("libicetray")
load("libdataio")

tray = I3Tray()

tray.AddModule("I3Reader","reader",
                Filename = "pass1.i3")

tray.AddModule("Dump","dump")

tray.AddModule("TrashCan","trash")

tray.Execute()
tray.Finish()

TODO Flush out these docs more fully.

Configuring modules with vectors

Python scripts can tersely configure modules with vectors of ints, doubles, strings, and OMKeys. Project “examples” contains a script “pass7_HelloConfiguration.py” which has an associated I3Module, HelloConfiguration, which demonstrates the use of all this

In a python script, an individual OMKey is created like this: OMKey(21,7). you pass it to a module like you might expect:

tray.AddModule("FryOM", "fry",
               OM = OMKey(3,3))

vectors of anythings are created by enclosing a comma separated list of anythings in square-brackets:

["strings", "in", "a", "row"]

and you pass these to a module like this:

tray.AddModule("ReverseTracks", "reverse",
               tracks = ["linefit", "dipolefit", "haystackfit"])

tray.AddModule("OMSelect", "select",
               oms = [OMKey(1,2), OMKey(3,4), OMKey(5,6)])

Python details for experts

There’s a gotcha. Python has lists, and it has tuples. ithon will convert either to an STL vector when it configures icetray, so this syntax will work too:

tray.AddModule("Jeopardy", "j",
  I'll_take="famous_numbers",
  for=500,
  famous_numbers=(0, 1, 3.14159, 1.618034
  )

here you’re implicitly creating a list: notice the parenthesis. But if you want to configure a vector with only one entry, it wont work:

famous_numbers=3.14159

here the parenthesis just disappear and that becomes just a double, fand you get a “cant convert parameter” error when configuring. But tuples stay tuples:

famous_numbers=[3.14159]

This works, and configures with a vector of length 1 containing pi. So just use [square brackets]. They mean the same thing and they’re easier to see.

NaN and Inf

I3Tray.py creates namespace-scope variables Inf and Nan, for the special floating-point values infinity and not-a-number. These are for the occasions when one needs to pass NaN or Inf to a module parameter, or to initialize e.g. an I3Double to NaN.

NaN compared to anything (including itself) is always false. To tell if a variable is nan, or not, use the functions isnan and isinf. In python 2.6 and later, these are in module math, in earlier versions they are in module scipy:

Python 2.6.2 (release26-maint, Apr 19 2009, 01:58:18)
[GCC 4.3.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from I3Tray import NaN, Inf
>>> NaN
nan
>>> Inf
inf
>>> NaN == NaN       # You probably do *not* want this
False
>>> import math
>>> math.isnan(NaN)  # You want this
True
>>> math.isinf(Inf)
True