input: Write a function to create a web API using Python and Flask that returns the current date and time. The API should be accessible at the '/datetime' route.
  
  from flask import Flask
  import datetime
  
  app = Flask(__name__)
  
  @app.route('/datetime')
  def get_datetime():
      return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
  
  if __name__ == '__main__':
      app.run(port=5000)
  
  assert get_datetime() == datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")
  assert app.config['DEBUG'] == None
  assert app.config['TESTING'] == False
output: @app.route('/datetime')
  def get_datetime():
      return datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S")