/data/refman/pasoursint/CMSSW_5_3_10/src/SimGeneral/Configuration/python/ThrowAndSetRandomRun.py

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import FWCore.ParameterSet.Config as cms

# function to modify an existing Cms Source in order to set the run number
# aimed at setting non trivial run number in MC production - be it GEN-SIM or DIGI step

def throwAndSetRandomRun(source,runsAndProbs):
        """Pass a list of tuple pairs, with the first item of the pair a run number
        and the second number of the pair a weight.  The function will normalize the
        weights so you do not have to worry about that.  The pairs will be used to randomly choose what Run
        should be assigned to the job.
        """
        from random import SystemRandom
        totalProb = 0.
        for r,p in runsAndProbs:
            totalProb+=p
        #this is the same random generator used to set the seeds for the RandomNumberGeneratorService
        random = SystemRandom()
        runProb = random.uniform(0,totalProb)
        sumProb = 0
        runNumber = 0
        for r,p in runsAndProbs:
            sumProb+=p
            if sumProb >= runProb:
                runNumber = r
                break
        print 'setting runNumber to: ',runNumber
        if source.type_() == "PoolSource":
            source.setRunNumber = cms.untracked.uint32(runNumber)
        else:
            #sources that inherit from ConfigurableInputSource use 'firstRun'
            source.firstRun = cms.untracked.uint32(runNumber)

        return