old_contents: import sys
  
  from exit import err_exit
  
  
  class Python(object):
      """Python interpreter abstraction."""
  
      def __init__(self, python=None, version_info=None):
          self.python = sys.executable
          self.version_info = sys.version_info
          if python is not None:
              self.python = python
          if version_info is not None:
              self.version_info = version_info
  
      def __str__(self):
          return self.python
  
      def is_valid_python(self):
          return (self.version_info[:2] >= (2, 6) and
                  self.version_info[:2] < (3, 0))
  
      def check_valid_python(self):
          if not self.is_valid_python():
              err_exit('Python 2.6 or 2.7 required')
  
new_contents: import sys
  
  from exit import err_exit
  
  
  class Python(object):
      """Python interpreter abstraction."""
  
      def __init__(self, python=None, version_info=None):
          self.python = python or sys.executable
          self.version_info = version_info or sys.version_info
  
      def __str__(self):
          return self.python
  
      def is_valid_python(self):
          return (self.version_info[:2] >= (2, 6) and
                  self.version_info[:2] < (3, 0))
  
      def check_valid_python(self):
          if not self.is_valid_python():
              err_exit('Python 2.6 or 2.7 required')
  
  
subject: Use terser idiom for initialization.