input: Write a function to simulate a rock-paper-scissors game, taking two player choices (rock, paper, or scissors) as inputs and returning the result indicating if it is a draw, or which player wins. The function should use predefined rules where 'rock' beats 'scissors', 'scissors' beat 'paper', and 'paper' beats 'rock'.
  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('paper', 'rock')=='Player 1 wins!'
  assert play_game('scissors', 'paper')=='Player 1 wins!'
  assert play_game('rock', 'rock')=='It is a draw!'
  assert play_game('scissors', 'rock')=='Player 2 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!'