注意：要想在python脚本中访问mysql，必须不能使用mysql默认的密码，必须要手动修改下数据库的密码：
方法：

1. 进入到mysql中：

mysql -u root -p
回车

2. 修改mysql密码步骤：
   （注意：一定要use mysql;）

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| myflaskapp         |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.01 sec)

mysql> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> update user set password=password('test123') where user='root';
Query OK, 3 rows affected (0.06 sec)
Rows matched: 3  Changed: 3  Warnings: 0

3.配置数据库代码：

# from app import views
app = Flask(__name__)
# Config MySQL  https://flask-mysqldb.readthedocs.io/en/latest/
app.config['MYSQL_HOST'] = 'localhost'
app.config['MYSQL_USER'] = 'root'
app.config['MYSQL_PASSWORD'] = 'test123'
app.config['MYSQL_DB'] = 'myflaskapp'
app.config['MYSQL_CURSORCLASS'] = 'DictCursor'
# init MYSQL
mysql = MySQL(app)
'''
4.启动服务器

if name=='main':
app.secret_key = 'test123'
app.run(debug=True)

5. 此时因为也已经写好了连接mysql的代码：

User Register

@app.route('/register', methods=['GET', 'POST'])
def register():
form = RegisterForm(request.form)
if request.method == 'POST' and form.validate():
name = form.name.data
email = form.email.data
username = form.username.data
password = sha256_crypt.encrypt(str(form.password.data))
# Create cursor
cur = mysql.connection.cursor()

    # Execute query
    cur.execute("INSERT INTO users(name, email, username, password) VALUES(%s, %s, %s, %s)", (name, email, username, password))

    # Commit to DB
    mysql.connection.commit()

    # Close connection
    cur.close()

    flash('You are now registered and can log in', 'success')
    return redirect(url_for('index'))
return render_template('register.html', form=form)

6. 在页面上点击Register，会弹出来register.html页面，然后在页面行填写合适的信息后，点击submmit，mysql数据库中就会出现一条数据。