input: 
  from flask import Flask, jsonify, request
  
  app = Flask(__name__)
  
  users_db = []
  
  @app.route('/users', methods=['POST'])
  def create_user():
      new_user = request.json
      users_db.append(new_user)
      return jsonify({'message': 'User created'}), 201
  
  @app.route('/users', methods=['GET'])
  def get_all_users():
      return jsonify(users_db)
  
  @app.route('/users/<id>', methods=['GET'])
  def get_one_user(id):
      user = next((user for user in users_db if user['id'] == id), None)
      return jsonify(user) if user else ('User not found', 404)
  
  if __name__ == "__main__":
      app.run(debug=True)
  
output:     if not user:
          return jsonify({'message': 'User not found'}), 404
      return jsonify(user)