Flask App:在功能运行时更新进度条

Question

我正在Flask中构建一个相当简单的WebApp,它通过网站的API执行功能.我的用户使用其帐户网址和API令牌填写表单; 当他们提交表单时,我有一个python脚本,通过API从他们的帐户导出PDF.这个函数可能需要很长时间,所以我想在表单页面上显示一个引导进度条,指示脚本在进程中的位置.我的问题是如何在函数运行时更新进度条？这是我正在谈论的简化版本.

views.py:

@app.route ('/export_pdf', methods = ['GET', 'POST'])
def export_pdf():
    form = ExportPDF()
    if form.validate_on_submit():
      try:
        export_pdfs.main_program(form.account_url.data,
          form.api_token.data)
        flash ('PDFs exported')
        return redirect(url_for('export_pdf'))
      except TransportException as e:
        s = e.content
        result = re.search('<error>(.*)</error>', s)
        flash('There was an authentication error: ' + result.group(1))
      except FailedRequest as e:
        flash('There was an error: ' + e.error)
    return render_template('export_pdf.html', title = 'Export PDFs', form = form)

export_pdf.html:

{% extends "base.html" %}

{% block content %}
{% include 'flash.html' %}
<div class="well well-sm">
  <h3>Export PDFs</h3>
  <form class="navbar-form navbar-left" action="" method ="post" name="receipt">
    {{form.hidden_tag()}}
    <br>
    <div class="control-group{% if form.errors.account_url %} error{% endif %}">
      <label class"control-label" for="account_url">Enter Account URL:</label>
      <div class="controls">
        {{ form.account_url(size = 50, class = "span4")}}
        {% for error in form.errors.account_url %}
          <span class="help-inline">[{{error}}]</span><br>
        {% endfor %}
      </div>
    </div>
    <br>
    <div class="control-group{% if form.errors.api_token %} error{% endif %}">
      <label class"control-label" for="api_token">Enter API Token:</label>
      <div class="controls">
        {{ form.api_token(size = 50, class = "span4")}}
        {% for error in form.errors.api_token %}
          <span class="help-inline">[{{error}}]</span><br>
        {% endfor %}
      </div>
    </div>
    <br>
    <button type="submit" class="btn btn-primary btn-lg">Submit</button>
  <br>
  <br>
  <div class="progress progress-striped active">
  <div class="progress-bar"  role="progressbar" aria-valuenow="0" aria-valuemin="0" aria-valuemax="100" style="width: 0%">
    <span class="sr-only"></span>
  </div>
</form>
</div>
</div>
{% endblock %}

和export_pdfs.py:

def main_program(url, token):
    api_caller = api.TokenClient(url, token)
    path = os.path.expanduser('~/Desktop/'+url+'_pdfs/')
    pdfs = list_all(api_caller.pdf.list, 'pdf')
    total = 0
    count = 1
    for pdf in pdfs:
        total = total + 1
    for pdf in pdfs:
        header, body = api_caller.getPDF(pdf_id=int(pdf.pdf_id))
        with open('%s.pdf' % (pdf.number), 'wb') as f:
          f.write(body)
        count = count + 1
        if count % 50 == 0:
          time.sleep(1)

在最后一个函数中,我总共将导出的PDF数量,并在处理时持续计数.如何将当前进度发送到我的.html文件以适应进度条的'style ='标记？优选地,我可以在其他页面上为进度条重用相同的工具.如果我没有提供足够的信息,请告诉我.

Answer 1

正如其他人在评论中所建议的那样,最简单的解决方案是在另一个线程中运行导出功能,并让您的客户端使用其他请求获取进度信息.处理此特定任务有多种方法.根据您的需要,您可能会选择或多或少的复杂产品.

这是关于如何使用线程执行此操作的非常(非常)最小示例:

import random
import threading
import time

from flask import Flask


class ExportingThread(threading.Thread):
    def __init__(self):
        self.progress = 0
        super().__init__()

    def run(self):
        # Your exporting stuff goes here ...
        for _ in range(10):
            time.sleep(1)
            self.progress += 10


exporting_threads = {}
app = Flask(__name__)
app.debug = True


@app.route('/')
def index():
    global exporting_threads

    thread_id = random.randint(0, 10000)
    exporting_threads[thread_id] = ExportingThread()
    exporting_threads[thread_id].start()

    return 'task id: #%s' % thread_id


@app.route('/progress/<int:thread_id>')
def progress(thread_id):
    global exporting_threads

    return str(exporting_threads[thread_id].progress)


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

在索引路由(/)中,我们为每个导出任务生成一个线程,然后我们向该任务返回一个ID,以便客户端稍后可以使用进度路径(/ progress/[exports_thread])检索它.导出线程每次认为合适时都会更新其进度值.

在客户端,你会得到这样的东西(这个例子使用jQuery):

function check_progress(task_id, progress_bar) {
    function worker() {
        $.get('progress/' + task_id, function(data) {
            if (progress < 100) {
                progress_bar.set_progress(progress)
                setTimeout(worker, 1000)
            }
        })
    }
}

如上所述,这个例子非常简约,你应该采用稍微复杂的方法.通常,我们会将特定线程的进度存储在数据库或某种类型的缓存中,这样我们就不依赖于共享结构,从而避免了我的示例所带来的大部分内存和并发问题.

Redis(https://redis.io)是一种内存数据库存储,通常非常适合此类任务.它很好地与Python集成(https://pypi.python.org/pypi/redis).

Answer 2

我在本地主机上运行这个简单但具有教育意义的 Flask SSE 实现。要在 GAE 中处理第 3 方（用户上传）库：

1. lib创建一个以您的根路径命名的目录。
2. gevent将库目录复制到lib目录。

3. 将这些行添加到您的main.py：

   import sys
   sys.path.insert(0,'lib')
   

4. 就这样。如果您使用lib子文件夹中的目录，请使用相对引用：sys.path.insert(0, ../../blablabla/lib')

来自http://flask.pocoo.org/snippets/116/

# author: oskar.blom@gmail.com
#
# Make sure your gevent version is >= 1.0
import gevent
from gevent.wsgi import WSGIServer
from gevent.queue import Queue

from flask import Flask, Response

import time


# SSE "protocol" is described here: http://mzl.la/UPFyxY
class ServerSentEvent(object):

    def __init__(self, data):
        self.data = data
        self.event = None
        self.id = None
        self.desc_map = {
            self.data : "data",
            self.event : "event",
            self.id : "id"
        }

    def encode(self):
        if not self.data:
            return ""
        lines = ["%s: %s" % (v, k) 
                 for k, v in self.desc_map.iteritems() if k]

        return "%s\n\n" % "\n".join(lines)

app = Flask(__name__)
subscriptions = []

# Client code consumes like this.
@app.route("/")
def index():
    debug_template = """
     <html>
       <head>
       </head>
       <body>
         <h1>Server sent events</h1>
         <div id="event"></div>
         <script type="text/javascript">

         var eventOutputContainer = document.getElementById("event");
         var evtSrc = new EventSource("/subscribe");

         evtSrc.onmessage = function(e) {
             console.log(e.data);
             eventOutputContainer.innerHTML = e.data;
         };

         </script>
       </body>
     </html>
    """
    return(debug_template)

@app.route("/debug")
def debug():
    return "Currently %d subscriptions" % len(subscriptions)

@app.route("/publish")
def publish():
    #Dummy data - pick up from request for real data
    def notify():
        msg = str(time.time())
        for sub in subscriptions[:]:
            sub.put(msg)

    gevent.spawn(notify)

    return "OK"

@app.route("/subscribe")
def subscribe():
    def gen():
        q = Queue()
        subscriptions.append(q)
        try:
            while True:
                result = q.get()
                ev = ServerSentEvent(str(result))
                yield ev.encode()
        except GeneratorExit: # Or maybe use flask signals
            subscriptions.remove(q)

    return Response(gen(), mimetype="text/event-stream")

if __name__ == "__main__":
    app.debug = True
    server = WSGIServer(("", 5000), app)
    server.serve_forever()
    # Then visit http://localhost:5000 to subscribe 
    # and send messages by visiting http://localhost:5000/publish