My Python application doesn't communicate with MySQL inside docker. Can someone help me?

The connection is not succeeding in docker. Look at my settings:

Dockerfile

FROM python:3.8.5-alpineWORKDIR /appCOPY requirements.txt .RUN python3 -m pip install --upgrade pipRUN pip install -r requirements.txtCOPY . .CMD ["python3", "-m", "scraper"]

docker-compose.yml

   version: '3'    services:      python_app:        build:          context: .          dockerfile: Dockerfile        ports:          - '80:80'        links:          - 'mysql_db'        depends_on:          - mysql_db        networks:          - app-tier      mysql_db:        image: mysql:5.7        ports:          - '3307:3306'        environment:           MYSQL_ROOT_PASSWORD: 'flavio'          MYSQL_DATABASE: 'Vestibular'          MYSQL_USER: 'flavio'          MYSQL_PASSWORD: ''        networks:          - app-tier    networks:      app-tier:        driver: bridge

db.py

import mysql.connectordef insert_into_database(data):    print("Salvando no banco de dados")    aux = ""    for i, item in enumerate(data):        if i == len(data)-1:            aux += str(item)        else:            aux += f"{str(item)}, "    try:        connection = mysql.connector.connect(host='localhost',                                            database='Vestibular',                                            user='flavio',                                            password='')        cursor = connection.cursor()        stmt = "SHOW TABLES LIKE 'Candidates'"        cursor.execute(stmt)        result = cursor.fetchone()        mySql_Create_Table_Query = """CREATE TABLE Candidates (                              Id int(11) AUTO_INCREMENT NOT NULL,                             Name varchar(250) NOT NULL,                             Score varchar(250) NOT NULL,                             PRIMARY KEY (Id)) """        mySql_insert_query = f"""INSERT INTO Candidates (Name, Score)                             VALUES                             {aux}; """        if not result:            cursor.execute(mySql_Create_Table_Query)        cursor.execute(mySql_insert_query)        connection.commit()        print(cursor.rowcount, "Record inserted successfully into Candidates table")        cursor.close()    except mysql.connector.Error as error:        print("Failed to insert record into Candidates table {}".format(error))    finally:        if connection.is_connected():            connection.close()            print("MySQL connection is closed")