input: Write a function to implement a basic version control system in Python that keeps track of changes in the code. The function should define a class `VersionControl` with methods to commit changes and restore to a previous commit. If the log file is empty, the restore method should do nothing.
  
  class VersionControl:
      def __init__(self, lines):
          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))
          log_file.close()
   
      def restore(self):
          log_file = open("log_file.txt", "r")
          lines = log_file.readlines()
          to_mark = self.mark-1
   
          if lines:
              self.lines = lines[to_mark][lines[to_mark].index(":")+2:].strip()
          log_file.close()
  
  assert VersionControl(["a", "b", "c"]).commit()=="1: ['a', 'b', 'c']"
  assert VersionControl(["a", "b", "c"]).restore()==['a', 'b', 'c']
  assert VersionControl([]).commit()=="1: []"
  assert VersionControl([]).restore()==[]
  assert VersionControl(["a", "b", "c"]).commit()=="1: ['a', 'b', 'c']"
  assert VersionControl(["a", "b", "c"]).restore()==['a', 'b', 'c']
output: 
  class VersionControl:
      def __init__(self, lines):
          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()
          return str(self.mark) + ": " + str(self.lines)
   
      def restore(self):
          log_file = open("log_file.txt", "r")
          lines = log_file.readlines()
          to_mark = self.mark-1
   
          if lines:
              self.lines = eval(lines[to_mark][lines[to_mark].index(":")+2:].strip())
          log_file.close()
          return self.lines
  