flask_ Reqparse parser inheritance in restful

Sample code 1：

from flask import Flask
from flask_restful import reqparse, Api, Resource

app = Flask(__name__)
api = Api(app)

USERS = {
    'row1': {'name': 'aaa', 'rate': [70, 65]},
    'row2': {'name': 'bbb', 'rate': [80, 90, 68]},
    'row3': {'name': 'ccc', 'rate': [90, 80]},
}

parser = reqparse.RequestParser()
parser.add_argument('name', type=str, required=True)  # required=True  Mandatory 
parser.add_argument('rate', type=int, help='rate is a number', action='append')  # action='append'  Recheckable value 
parser.add_argument('User-Agent', type=str, location='headers')

# #  The parser inherits 
parser_copy = parser.copy()
parser_copy.add_argument('bar', type=int)
parser_copy.replace_argument('bar', type=str, required=True)
parser_copy.remove_argument('User-Agent')


#  Where the request is actually handled 
class UserInfo(Resource):
    def get(self):
        return USERS, 200

    def post(self):
        args = parser.parse_args()
        # args = parser_copy.parse_args()
        user_id = int(max(USERS.keys()).lstrip('row')) + 1
        user_id = 'row%i' % user_id
        USERS[user_id] = {'name': args['name'], 'rate': args['rate']}
        USERS[user_id]['ua'] = args.get('User-Agent')
        USERS[user_id]['bar'] = args.get('bar')
        return USERS[user_id], 201


api.add_resource(UserInfo, '/')

if __name__ == '__main__':
    app.run(debug=True)

Running results ：

  Sample code 2：     【 Pay attention to the sample code 1 The difference between 】

from flask import Flask
from flask_restful import reqparse, Api, Resource

app = Flask(__name__)
api = Api(app)

USERS = {
    'row1': {'name': 'aaa', 'rate': [70, 65]},
    'row2': {'name': 'bbb', 'rate': [80, 90, 68]},
    'row3': {'name': 'ccc', 'rate': [90, 80]},
}

parser = reqparse.RequestParser()
parser.add_argument('name', type=str, required=True)  # required=True  Mandatory 
parser.add_argument('rate', type=int, help='rate is a number', action='append')  # action='append'  Recheckable value 
parser.add_argument('User-Agent', type=str, location='headers')

# #  The parser inherits 
parser_copy = parser.copy()
parser_copy.add_argument('bar', type=int)
parser_copy.replace_argument('bar', type=str, required=True)
parser_copy.remove_argument('User-Agent')


#  Where the request is actually handled 
class UserInfo(Resource):
    def get(self):
        return USERS, 200

    def post(self):
        # args = parser.parse_args()
        args = parser_copy.parse_args()
        user_id = int(max(USERS.keys()).lstrip('row')) + 1
        user_id = 'row%i' % user_id
        USERS[user_id] = {'name': args['name'], 'rate': args['rate']}
        USERS[user_id]['ua'] = args.get('User-Agent')
        USERS[user_id]['bar'] = args.get('bar')
        return USERS[user_id], 201


api.add_resource(UserInfo, '/')

if __name__ == '__main__':
    app.run(debug=True)

Running results ：