new_contents: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  """Installs dependencies appropriate for the Python version."""
  import subprocess
  import sys
  
  subprocess.call("pip", "install --use-mirrors -r requirements.txt")
  if sys.version_info[0] >= 3: # Python 3
      # No Python 3-specific dependencies right now
      pass
  else:  # Python 2
      subprocess.call("pip", "install --use-mirrors unittest2")
  
subject: Install different deps for Python 3 vs. Python 2.