input: Write a function to determine the winner in a rock-paper-scissors game given the choices of two players. The function takes two arguments: player1 and player2, which are strings representing the choices 'rock', 'paper', or 'scissors'. The function should return a string indicating the result: 'It is a draw!' if both players make the same choice, 'Player 1 wins!' if player1 defeats player2 according to the rules, and 'Player 2 wins!' if player2 defeats player1.
  
  def play_game(player1, player2):
      rules = {'rock': 'scissors', 'scissors': 'paper', 'paper': 'rock'}
      if player1 == player2:
          return 'It is a draw!'
      elif rules[player1] == player2:
          return 'Player 1 wins!'
      elif rules[player2] == player1:
          return 'Player 2 wins!'
  
  assert play_game('rock', 'scissors') == 'Player 1 wins!'
  assert play_game('scissors', 'rock') == 'Player 2 wins!'
  assert play_game('paper', 'paper') == 'It is a draw!'
  assert play_game('rock', 'paper') == 'Player 2 wins!'
  assert play_game('scissors', 'paper') == 'Player 1 wins!'
output: def play_game(player1, player2):
      rules = {'rock': 'scissors', 'scissors': 'paper', 'paper': 'rock'}
      if player1 == player2:
          return 'It is a draw!'
      elif rules[player1] == player2:
          return 'Player 1 wins!'
      elif rules[player2] == player1:
          return 'Player 2 wins!'