flask web开发创建虚拟博客文章数据bug AttributeError: 'NoneType' object has no attribute 'encode'的解决

该书第11.3.1节末尾说运行程序会看到首页显示了很长的随机博客文章列表。但是我运行程序却提示出现AttributeError: 'NoneType' object has no attribute 'encode'，然后我运行github作者源码，也出现了这个bug（如下）

Traceback (most recent call last):File "E:\flalearn\venv\lib\site-packages\flask\app.py", line 1997, in callreturn self.wsgi_app(environ, start_response)File "E:\flalearn\venv\lib\site-packages\flask\app.py", line 1985, in wsgi_appresponse = self.handle_exception(e)File "E:\flalearn\venv\lib\site-packages\flask\app.py", line 1540, in handle_exceptionreraise(exc_type, exc_value, tb)File "E:\flalearn\venv\lib\site-packages\flask\app.py", line 1982, in wsgi_appresponse = self.full_dispatch_request()File "E:\flalearn\venv\lib\site-packages\flask\app.py", line 1614, in full_dispatch_requestrv = self.handle_user_exception(e)File "E:\flalearn\venv\lib\site-packages\flask\app.py", line 1517, in handle_user_exceptionreraise(exc_type, exc_value, tb)File "E:\flalearn\venv\lib\site-packages\flask\app.py", line 1612, in full_dispatch_requestrv = self.dispatch_request()File "E:\flalearn\venv\lib\site-packages\flask\app.py", line 1598, in dispatch_requestreturn self.view_functionsrule.endpointFile "E:\flalearn\app\main\views.py", line 22, in indexreturn render_template('index.html', form = form, posts = posts)File "E:\flalearn\venv\lib\site-packages\flask\templating.py", line 134, in render_templatecontext, ctx.app)File "E:\flalearn\venv\lib\site-packages\flask\templating.py", line 116, in _renderrv = template.render(context)File "E:\flalearn\venv\lib\site-packages\jinja2\environment.py", line 1008, in renderreturn self.environment.handle_exception(exc_info, True)File "E:\flalearn\venv\lib\site-packages\jinja2\environment.py", line 780, in handle_exceptionreraise(exc_type, exc_value, tb)File "E:\flalearn\app\templates\index.html", line 3, in top-level template code{% import "_macros.html" as macros %}File "E:\flalearn\app\templates\base.html", line 1, in top-level template code{% extends "bootstrap/base.html" %}File "E:\flalearn\venv\lib\site-packages\flask_bootstrap\templates\bootstrap\base.html", line 1, in top-level template code{% block doc -%}File "E:\flalearn\venv\lib\site-packages\flask_bootstrap\templates\bootstrap\base.html", line 4, in block "doc"{%- block html %}File "E:\flalearn\venv\lib\site-packages\flask_bootstrap\templates\bootstrap\base.html", line 20, in block "html"{% block body -%}File "E:\flalearn\venv\lib\site-packages\flask_bootstrap\templates\bootstrap\base.html", line 23, in block "body"{% block content -%}File "E:\flalearn\app\templates\base.html", line 62, in block "content"{% block page_content %}{% endblock %}File "E:\flalearn\app\templates\index.html", line 16, in block "page_content"{% include '_posts.html' %}File "E:\flalearn\app\templates_posts.html", line 6, in top-level template codeFile "E:\flalearn\app\models.py", line 184, in gravatarself.email.encode('utf-8')).hexdigest()AttributeError: 'NoneType' object has no attribute 'encode'

原因：练习前面章节时向data-dev.sqlite添加了用户，但对这些用户没设置邮箱，导致User类的gravatar方法处运行出现错误。解决办法1：设置if self.email（如下）。方法2：在数据库中给用户手动设置邮箱。

def gravatar(self, size = 100, default = 'identicon', rating = 'g'):if request.is_secure:url = 'https://secure.gravatar.com/avatar'else:url = 'http://www.gravatar.com/avatar'if self.email:hash = self.avatar_hash or hashlib.md5(self.email.encode('utf-8')).hexdigest()return '{url}/{hash}?s={size}&d={default}&r={rating}'.format(url=url, hash=hash, size=size, default=default, rating=rating)