Flask報(bào)錯(cuò)jinja2:expected token 'end of statement block', got 'as'

用Flask寫，到了往前端頁(yè)面 render_template（）數(shù)據(jù)這一步，突然開始作死式的報(bào)錯(cuò)，怎么調(diào)后端都沒(méi)用；哪位大神幫忙找出原因，謝謝
報(bào)錯(cuò)：

前端模板：“index.html”

{% extends "base.html" %}
{% extends "bootstrap/wtf.html" as wtf %}
{% block title %} Hello {% endblock %}
{% block page_content %}
<div class="page-header">
    <h1>Hello,{% if name %}{{ name }}{% else %}Stranger{% endif %}!</h1>
</div>
{{ wtf.quick_form(form) }}
{% endblock %}

后端文件："Hello.py"

from flask import Flask
from flask import render_template
from flask_bootstrap import Bootstrap
from flask_moment import Moment
# from datetime import datetime
# from flask import abort
from flask_script import Manager
from flask_wtf import Form
from wtforms import StringField,SubmitField
from wtforms.validators import DataRequired

app = Flask(__name__)
app.config["SECRET_KEY"] = "hard to guess string" #設(shè)置Flask-WTF
manager = Manager(app)
bootstrap = Bootstrap(app)  #初始化Flask-Boorstrap
moment = Moment(app)        #初始化Flask-Moment
#定義表單類
class NameForm(Form):
    name = StringField("What is your name?",validators=[DataRequired()])
    submit = SubmitField("Submit")




@app.errorhandler(404)
def page_not_found(e):
    return render_template("404.html"),404

@app.errorhandler(500)
def internal_server_error(e):
    return render_template("500.html"),500

@app.route('/',methods = ["GET","POST"])
def index():
    name = None
    form = NameForm()
    if form.validate_on_submit():
        name = form.name.data
        form.name.data = ""
    return render_template("index.html")

if __name__ == '__main__':
# app.run(host = "0.0.0.0")
    app.run(debug = True)