new_contents: #!/usr/bin/env python
  # http://www.mojidong.com/python/2013/05/10/python-exec-eval/
  
  a = 1
  print(eval("a + 1"))
  
  a = 1
  g = {
      'a': 10
  }
  print(eval("a + 1", g))
  
  a = 10
  b = 20
  c = 20
  g = {
      'a': 6,
      'b': 8
  }
  l = {
      'b': 9,
      'c': 10
  }
  print(eval("a+b+c", g, l))
  
  print(eval('abs(a)',{'__builtins__':__builtins__, 'a':-1}))
  # eval('abs(a)',{'__builtins__':None, 'a':-1})
  
subject: add eval