Grabbing output of Root command

ROOT
1

Hello,

I’m trying to grab (and parse) the output of a root command.

#! /usr/bin/env python

import sys

# a simple class with a write method
class WritableObject:
    def __init__ (self):
        self.content = []
    def write (self, string):
        self.content.append(string)


myOutput = WritableObject()                   # a writable object
sys.stdout = myOutput                       # redirection
# sys.stderr = myOutput


import ROOT
rootfile = ROOT.TFile.Open ('somefile.root')
tree = rootfile.Get('Events')

print "Hi mom.obj ="
tree.Print()
sys.stdout = sys.__stdout__              # remember to reset sys.stdout!
#sys.stderr = sys.__stderr__

print "Done"

print myOutput.content

When I run this, the ‘Hi mom.obj’ gets caught in myOutput, but the ‘Print()’ command goes to the screen and is not redirected.

How can I do this?

Thanks,
Charles

2

Charles,

in order to also grab the output from C++, you’ll need to dup the file descriptor and redirect it. This is the basic idea:[code]#! /usr/bin/env python
import sys

class Redirector( object ):
def init( self, stream ):
import os, sys, tempfile
w, n = tempfile.mkstemp()
os.unlink( n )
self._file = os.fdopen( w, ‘rw’ )
self._stream = stream

  self._savefn = os.dup( self._stream.fileno() )
  os.dup2( self._file.fileno(), self._stream.fileno() )

def restore( self ):
import os

  self._stream.flush()
  os.dup2( self._savefn, self._stream.fileno() )

  self._file.seek( 0 )
  content = ''.join( self._file.readlines() )
  self._file.close()
  del self._file, self._savefn, self._stream

  return content

import ROOT
rootfile = ROOT.TFile.Open (‘somefile.root’)
tree = rootfile.Get(‘Events’)

r = Redirector( sys.stdout )
tree.Print()
print r.restore()[/code]
I’m not sure whether it can be done easily without redirecting to a temporary file.

HTH,
Wim