《Flask Web开发》学习笔记之bug--（5）【jinja2.exceptions.TemplateSyntaxError: Encountered unknown tag 'endlock'】

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在阅读《Flask Web开发》过程中遇到一个模板语法错误，详细报错为`jinja2.exceptions.TemplateSyntaxError: Encountered unknown tag 'endlock'`。本文记录了这个问题的出现原因及解决方案，帮助读者避免类似问题。

# hello.py

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

class NameForm(Form):
	name = StringField('What is your name?', validators=[Required])
	submit = SubmitField('Submit')
		

app = Flask(__name__)

app.config['SECRET_KEY'] = 'hard to guess string'
manager = Manager(app)
bootstrap = Bootstrap(app)
moment = Moment(app)

@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('/')
def index():
	return render_template('index.html', current_time=datetime.utcnow())

@app.route('/user/<name>')
def user(name):
	return render_template('user.html', name=name)


if __name__ == '__main__':
	manager.run()

{% extends "base.html" %}

{% block title %}Flasky - Internal Server Error{% endblock %}

{% block page_content %}
<div class="page-header">
	<h1>Internal Server Error</h1>
</div>
{% endlock %}

$ python3 hello.py runserver --host 0.0.0.0

报错信息：

* Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
[2017-07-13 14:17:47,740] ERROR in app: Exception on / [GET]
Traceback (most recent call last):
  File "/home/henry/.local/lib/python3.5/site-packages/flask/app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/henry/.local/lib/python3.5/site-packages/flask/app.py", line 1614, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/henry/.local/lib/python3.5/site-packages/flask/app.py", line 1517, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/henry/.local/lib/python3.5/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/home/henry/.local/lib/python3.5/site-packages/flask/app.py", line 1612, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/henry/.local/lib/python3.5/site-packages/flask/app.py", line 1598, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "hello.py", line 32, in index
    return render_template('index.html', current_time=datetime.utcnow())
  File "/home/henry/.local/lib/python3.5/site-packages/flask/templating.py", line 134, in render_template
    context, ctx.app)
  File "/home/henry/.local/lib/python3.5/site-packages/flask/templating.py", line 116, in _render
    rv = template.render(context)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/environment.py", line 1008, in render
    return self.environment.handle_exception(exc_info, True)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/environment.py", line 780, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/_compat.py", line 37, in reraise
    raise value.with_traceback(tb)
  File "/home/henry/dev/Flask_Web_Python_Henry/flask_henry/templates/index.html", line 2, in top-level template code
    {% import "bootstrap/wtf.html" as wtf %}
  File "/home/henry/dev/Flask_Web_Python_Henry/flask_henry/templates/base.html", line 1, in top-level template code
    {% extends "bootstrap/base.html" %}
  File "/home/henry/.local/lib/python3.5/site-packages/flask_bootstrap/templates/bootstrap/base.html", line 1, in top-level template code
    {% block doc -%}
  File "/home/henry/.local/lib/python3.5/site-packages/flask_bootstrap/templates/bootstrap/base.html", line 4, in block "doc"
    {%- block html %}
  File "/home/henry/.local/lib/python3.5/site-packages/flask_bootstrap/templates/bootstrap/base.html", line 20, in block "html"
    {% block body -%}
  File "/home/henry/.local/lib/python3.5/site-packages/flask_bootstrap/templates/bootstrap/base.html", line 23, in block "body"
    {% block content -%}
  File "/home/henry/dev/Flask_Web_Python_Henry/flask_henry/templates/base.html", line 35, in block "content"
    {% block page_content %}{% endblock %}
  File "/home/henry/dev/Flask_Web_Python_Henry/flask_henry/templates/index.html", line 10, in block "page_content"
    {{ wtf.quick_form(form) }}
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/runtime.py", line 553, in _invoke
    rv = self._func(*arguments)
  File "/home/henry/.local/lib/python3.5/site-packages/flask_bootstrap/templates/bootstrap/wtf.html", line 200, in template
    {{ form.hidden_tag() }}
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/environment.py", line 430, in getattr
    return getattr(obj, attribute)
jinja2.exceptions.UndefinedError: 'form' is undefined
127.0.0.1 - - [13/Jul/2017 14:17:47] "GET / HTTP/1.1" 500 -
Error on request:
Traceback (most recent call last):
  File "/home/henry/.local/lib/python3.5/site-packages/werkzeug/serving.py", line 209, in run_wsgi
    execute(self.server.app)
  File "/home/henry/.local/lib/python3.5/site-packages/werkzeug/serving.py", line 197, in execute
    application_iter = app(environ, start_response)
  File "/home/henry/.local/lib/python3.5/site-packages/flask/app.py", line 1997, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/henry/.local/lib/python3.5/site-packages/flask/app.py", line 1985, in wsgi_app
    response = self.handle_exception(e)
  File "/home/henry/.local/lib/python3.5/site-packages/flask/app.py", line 1547, in handle_exception
    return self.finalize_request(handler(e), from_error_handler=True)
  File "/home/henry/dev/Flask_Web_Python_Henry/flask_henry/hello.py", line 28, in internal_server_error
    return render_template('500.html'), 500
  File "/home/henry/.local/lib/python3.5/site-packages/flask/templating.py", line 133, in render_template
    return _render(ctx.app.jinja_env.get_or_select_template(template_name_or_list),
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/environment.py", line 869, in get_or_select_template
    return self.get_template(template_name_or_list, parent, globals)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/environment.py", line 830, in get_template
    return self._load_template(name, self.make_globals(globals))
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/environment.py", line 804, in _load_template
    template = self.loader.load(self, name, globals)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/loaders.py", line 125, in load
    code = environment.compile(source, name, filename)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/environment.py", line 591, in compile
    self.handle_exception(exc_info, source_hint=source_hint)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/environment.py", line 780, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/_compat.py", line 37, in reraise
    raise value.with_traceback(tb)
  File "/home/henry/dev/Flask_Web_Python_Henry/flask_henry/templates/500.html", line 9, in template
    {% endlock %}
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/environment.py", line 497, in _parse
    return Parser(self, source, name, encode_filename(filename)).parse()
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 896, in parse
    result = nodes.Template(self.subparse(), lineno=1)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 878, in subparse
    rv = self.parse_statement()
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 130, in parse_statement
    return getattr(self, 'parse_' + self.stream.current.value)()
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 268, in parse_block
    node.body = self.parse_statements(('name:endblock',), drop_needle=True)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 165, in parse_statements
    result = self.subparse(end_tokens)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 878, in subparse
    rv = self.parse_statement()
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 144, in parse_statement
    self.fail_unknown_tag(token.value, token.lineno)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 97, in fail_unknown_tag
    return self._fail_ut_eof(name, self._end_token_stack, lineno)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 90, in _fail_ut_eof
    self.fail(' '.join(message), lineno)
  File "/home/henry/.local/lib/python3.5/site-packages/jinja2/parser.py", line 59, in fail
    raise exc(msg, lineno, self.name, self.filename)
jinja2.exceptions.TemplateSyntaxError: Encountered unknown tag 'endlock'. Jinja was looking for the following tags: 'endblock'. The innermost block that needs to be closed is 'block'.

闭合处应该是【endblock】，少写了一个字母【b】