Filling variable-sized branches in PyROOT

[Andrea91]

Hi,
I am filling a tree in pyROOT (root version 6.08). It does the job, doesn’t give any errors, but when I look at the values in TBrowser, all the variable-sized branches have values that are completely off from what I expect them to be (10^33 instead of 10^3).
Here is a snippet of the code I use:

class DigitToTree(Module):
  def initialize(self):
    print("Initializing DigitToTree module.")

    self.f = TFile(OUTPUT, 'RECREATE')
    self.t = TTree('tree', 'Tree with plain data from ECLCalDigits')
    self.evtn = array('f', [0])
    self.cellID   = array('f', [0])
    self.energy  = array('f', [0])
    self.energy_sum = array('f', [0])
    self.time = array('f', [0])
    self.nentries = array('i', [0])
    self.cal = array('i', [0])

    self.t.Branch('evtn', self.evtn, 'evtn/F')
    self.t.Branch('nentries', self.nentries, 'nentries/I')
    self.t.Branch('energy_sum', self.energy_sum, 'energy_sum/F')
    self.t.Branch('cellID', self.cellID, 'cellID[nentries]/F')
    self.t.Branch('energy', self.energy, 'energy[nentries]/F')
    self.t.Branch('time', self.time, 'time[nentries]/F')
    self.t.Branch('isCalibrated', self.cal, 'isCalibrated/I')

  def terminate(self):
    print("Finalizing DigitToTree module.")
    self.f.Write()
    self.f.Close()

  '''
  Convert ECLDigit data to simple ROOT Tree
  '''
  def event(self):
    '''
    Do conversion
    '''
    digits = PyStoreArray('ECLCalDigits')

    self.evtn[0] += 1
    self.energy_sum[0] = 0
    self.nentries[0] = digits.getEntries()
    print(digits.getEntries())
    print('###############')
    self.cal[0] = 0

    for i in range(digits.getEntries()):
      self.energy_sum[0] += digits[i].getEnergy()

    included = getEventInclusions(digits, self.evtn[0])

    for i in range(digits.getEntries()):
      if (not included[i]): continue
      self.cellID.insert(i, digits[i].getCellId())
      self.energy.insert(i, digits[i].getEnergy())
      self.time.insert(i, digits[i].getTime())
      if (digits[i].isCalibrated()):
        self.cal[0] = 1
      else:
        self.cal[0] = 0
      
    self.t.Fill()
    
    print(self.cellID)
    del self.energy[:]
    del self.cellID[:]
    del self.time[:]

Branches ‘cellID’, ‘energy’ and ‘time’ are the problematic ones.
Any ideas of what went wrong?

[wlav]

The insert() calls require the memory held by the array objects to grow. This works by allocating a new buffer of the right size, copying over the old values, then deleting the old buffer. After insert(), the TTree thus holds a pointer to deleted memory. You’ll need to reset the branch address every time the array resizes, or make it big enough straight off the bat.

[Andrea91]

Thanks for your reply. Can you maybe show me an example for how to do that?

[wlav]

Creating a larger array is a simple matter of using array(‘f’, [0]*size) with ‘size’ set to the desired size. For the ROOT side, presumably using t.SetBranchAddress() should work (haven’t tried; I don’t have ROOT installed anymore).