13 About Responses
view function会自动转换返回对象类型为response
1 如果返回值为string，那么返回值作为参数创建一个response
2 如果返回值为tuple，例如 (response, status, headers) or (response, headers)
make_response()会创建一个response
14 Sessions
除了request可以store information，其包括由一个请求到下一个。另外一个是object session。
app.secret_key = b'_5#y2L"F4Q8z\n\xec][/'
@app.route('/')
def index():
if 'username' in session:
return 'logined in as %s' % escape(session['username'])
return 'you are not logged in'
@app.route('/login', methods=['GET', 'POST'])
def login():
if request.method == 'POST':
session['username'] = request.form['username']
return redirect(url_for('index'))
else:
return '''
<form method="post">
<p><input type=text name=username>
<p><input type=submit value=Login>
</form>
'''
@app.route('/logout')
def logout():
if session['username']: #direct run session exception，KeyError: 'username'
#if not exist，return None，which not need if aboved
session.pop('username',None)
return redirect(url_for('index'))