input: Write a function that edits the given Python program to print 'Happy Holidays' 10 times. The function should take in a Python code string and modify it to print 'Happy Holidays' instead of 'Hello World'.
  
  assert modify_program("for i in range(10):\n    print('Hello World')")=="for i in range(10):\n    print('Happy Holidays')"
  assert modify_program("")==""
  assert modify_program("print('Hello World')")=="print('Hello World')"
  assert modify_program("for i in range(5):\n    print('Hello World')\nfor i in range(10):\n    print('Hello World')")=="for i in range(5):\n    print('Hello World')\nfor i in range(10):\n    print('Happy Holidays')"
output: def modify_program(code):
      lines = code.split('\n')
      for i in range(len(lines)):
          if "print('Hello World')" in lines[i]:
              lines[i] = lines[i].replace("print('Hello World')", "print('Happy Holidays')")
      return '\n'.join(lines)