import subprocess
import sys

opt = subprocess.run( [ 'opt', '-passes=print<loops>','-disable-output', sys.argv[1]], stdout=subprocess.PIPE, stderr=subprocess.PIPE )

stdout = opt.stdout.decode()

pattern = 'Loop at depth 1 containing'

if (pattern in opt.stderr.decode()):
  print('This is interesting!')
  sys.exit(0)
else:
  print('This is NOT interesting!')
  sys.exit(1)