input: 
  from typing import List
  
  class VersionControl:
      """
      A basic version control system that keeps track of changes in the code.
      >>> vc = VersionControl([1, 2, 3])
      >>> vc.commit()
      >>> vc.commit()
      >>> vc.restore()
      >>> vc.lines
      '2: [1, 2, 3]'
      """
      def __init__(self, lines: List):
          self.lines = lines
          self.mark = 0
   
      def commit(self):
          self.mark += 1
          log_file = open("log_file.txt", "a+")
          log_file.write(str(self.mark) + ": " + str(self.lines) + "\n")
          log_file.close()
   
      def restore(self):
          log_file = open("log_file.txt", "r")
          lines = log_file.readlines()
          to_mark = self.mark-1
   
          self.lines = lines[to_mark].strip()
          log_file.close()
  
output:     def restore(self):
          log_file = open("log_file.txt", "r")
          lines = log_file.readlines()
          to_mark = self.mark-1
          if to_mark >= 0 and to_mark < len(lines):
              self.lines = lines[to_mark].strip()
          else:
              self.lines = "No previous version available"
          log_file.close()