input: Write a python function to create a Flask app that has routes to handle GET, POST, PUT, and DELETE requests for items.
  assert get_items() == 'All items'
  assert create_item('Item1') == 'Item created'
  assert get_item(1) == 'Item1'
  assert update_item(1, 'UpdatedItem1') == 'Item updated'
  assert delete_item(1) == 'Item deleted'
output: from flask import Flask, request, jsonify
  
  app = Flask(__name__)
  
  items = {}
  
  @app.route('/items', methods=['GET'])
  def get_items():
      return jsonify(list(items.values()))
  
  @app.route('/items', methods=['POST'])
  def create_item():
      item = request.json.get('item')
      item_id = len(items) + 1
      items[item_id] = item
      return 'Item created', 201
  
  @app.route('/items/<int:item_id>', methods=['GET'])
  def get_item(item_id):
      item = items.get(item_id)
      if item:
          return jsonify(item)
      else:
          return 'Item not found', 404
  
  @app.route('/items/<int:item_id>', methods=['PUT'])
  def update_item(item_id):
      item = request.json.get('item')
      if item_id in items:
          items[item_id] = item
          return 'Item updated', 200
      else:
          return 'Item not found', 404
  
  @app.route('/items/<int:item_id>', methods=['DELETE'])
  def delete_item(item_id):
      if item_id in items:
          del items[item_id]
          return 'Item deleted', 200
      else:
          return 'Item not found', 404
  
  if __name__ == '__main__':
      app.run(debug=True)