input: Write a function to generate a REST API with Python and Flask that allows users to create, read, update, and delete records from a database. The function should return the Flask app instance.
  assert generate_rest_api()==<flask.app.Flask at 0x7f8d4c0b9c10>
output: from flask import Flask, request, jsonify
  from flask_sqlalchemy import SQLAlchemy
  
  def generate_rest_api():
      app = Flask(__name__)
      app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
      db = SQLAlchemy(app)
  
      class Record(db.Model):
          id = db.Column(db.Integer, primary_key=True)
          data = db.Column(db.String(80), nullable=False)
  
          def to_dict(self):
              return {'id': self.id, 'data': self.data}
  
      @app.route('/records', methods=['POST'])
      def create_record():
          data = request.json.get('data')
          if not data:
              return jsonify({'error': 'Data is required'}), 400
          new_record = Record(data=data)
          db.session.add(new_record)
          db.session.commit()
          return jsonify(new_record.to_dict()), 201
  
      @app.route('/records', methods=['GET'])
      def read_records():
          records = Record.query.all()
          return jsonify([record.to_dict() for record in records])
  
      @app.route('/records/<int:id>', methods=['GET'])
      def read_record(id):
          record = Record.query.get(id)
          if record is None:
              return jsonify({'error': 'Record not found'}), 404
          return jsonify(record.to_dict())
  
      @app.route('/records/<int:id>', methods=['PUT'])
      def update_record(id):
          record = Record.query.get(id)
          if record is None:
              return jsonify({'error': 'Record not found'}), 404
          data = request.json.get('data')
          if not data:
              return jsonify({'error': 'Data is required'}), 400
          record.data = data
          db.session.commit()
          return jsonify(record.to_dict())
  
      @app.route('/records/<int:id>', methods=['DELETE'])
      def delete_record(id):
          record = Record.query.get(id)
          if record is None:
              return jsonify({'error': 'Record not found'}), 404
          db.session.delete(record)
          db.session.commit()
          return jsonify({'result': True})
  
      with app.app_context():
          db.create_all()
  
      return app