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我发现在烧瓶的返回语句中链接几种方法可能存在错误。我想看看是否有人对如何解决这个问题有任何建议。

这是我的代码：

#!/usr/bin/env python

import flask
import time
from itertools import chain
from pygraphviz import AGraph

class TestClass(object):

    def __init__(self):
        G = ''

    def worker(self):
    a='1234'
        b=a + '45\n'
        yield b
        time.sleep(3)
        yield a

    def worker2(self):
        time.sleep(3)
        c = '\n9876'
        yield c

    def graph(self):
        G = AGraph(overlap='false')

tc = TestClass()
app = flask.Flask(__name__)


@app.route('/')
def test_method_get_stuff():
    return flask.render_template('index.html')

@app.route('/', methods=['POST'])
def test_method_post_stuff():
    def test_method_sub_function():
    return chain(tc.worker(), tc.worker2(),tc.graph())
    return flask.Response(test_method_sub_function(),mimetype= 'text/plain')

app.run(debug=True)

一旦请求一个帖子tc.worker()，tc.worker2()生成器就会正确返回，但一旦它尝试执行tc.graph()它，就会出现以下错误。

 * Running on http://127.0.0.1:5000/
 * Restarting with reloader
127.0.0.1 - - [17/Aug/2014 18:23:17] "GET / HTTP/1.1" 200 -
127.0.0.1 - - [17/Aug/2014 18:23:18] "POST / HTTP/1.1" 200 -
Debugging middleware caught exception in streamed response at a point where response headers were already sent.
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/werkzeug/wsgi.py", line 691, in __next__
    return self._next()
  File "/usr/lib/python2.7/site-packages/werkzeug/wrappers.py", line 81, in _iter_encoded
    for item in iterable:
TypeError: 'NoneType' object is not iterable
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