title: ImportError raised when trying to load 'bootstrap3.templatetags.bootstrap3': cannot import name 'flatatt'
body: <p>I create a project use django, and the upload it to heroku.</p>
  
  <p>It can run successfully in local environment, and functions can also work well. I upload successfully without any problems, but when I visit it in heroku(<a href="https://APP_NAME.herokuapp.com/" rel="nofollow noreferrer">https://APP_NAME.herokuapp.com/</a>), it have some issues like this:</p>
  
  <pre><code>InvalidTemplateLibrary at /
  
  Invalid template library specified. ImportError raised when trying to load 'bootstrap3.templatetags.bootstrap3': cannot import name 'flatatt'
  
  Request Method:
  GET
  Request URL:
  https://APP_NAME.herokuapp.com/
  Django Version:
  2.0.2
  Exception Type:
  InvalidTemplateLibrary
  Exception Value:
  Invalid template library specified. ImportError raised when trying to load 'bootstrap3.templatetags.bootstrap3': cannot import name 'flatatt'
  Exception Location:
  /app/.heroku/python/lib/python3.6/site-packages/django/template/backends/django.py in get_package_libraries, line 125
  Python Executable:
  /app/.heroku/python/bin/python
  Python Version:
  3.6.4
  Python Path:
  ['/app',
   '/app/.heroku/python/bin',
   '/app',
   '/app/.heroku/python/lib/python36.zip',
   '/app/.heroku/python/lib/python3.6',
   '/app/.heroku/python/lib/python3.6/lib-dynload',
   '/app/.heroku/python/lib/python3.6/site-packages']
  Server time:
  Sun, 25 Feb 2018 02:19:09 +0000
  </code></pre>
  
  <p>I tried to use django-bootstrap4, but it also have deployment problems with django-bootstrap3.</p>
  
  <p>How can I do?</p>
  
  <p>Thanks a lot.</p>
  
  <hr>
  
  <p>update:</p>
  
  <ul>
  <li><p>requirements.txt</p>
  
  <p>pip freeze > requirements.txt</p></li>
  </ul>
  
  <p>The requirements.txt contents like this:</p>
  
  <pre><code>dj-database-url==0.4.2
  Blockquote
  django==2.0.2
  -e git+https://git.heroku.com/APP_NAME.git@cbb5b522d**SECRET**710#egg=django_bootstrap3
  gunicorn==19.7.1
  psycopg2-binary==2.7.4
  pytz==2017.3
  whitenoise==3.3.1
  </code></pre>
  
  <p>NOTICE:
  That is the originial file.I modified the 4th line to  a certain version,like <code>django-bootstrap3==6.2.2</code>.</p>
  
  <ul>
  <li>bootstrap3 settings</li>
  </ul>
  
  <p>Some settings to reference in my virtual-environment:</p>
  
  <p><code>ll_env/Lib/site-packages/bootstrap3/bootstrap.py</code></p>
  
  <pre><code># -*- coding: utf-8 -*-
  from __future__ import unicode_literals
  from importlib import import_module
  ...
  </code></pre>
  
  <p><code>ll_env/Lib/site-packages/bootstrap3/utils.py</code></p>
  
  <pre><code>from django.forms.utils import flatatt
  from django.template import Variable, VariableDoesNotExist
  from django.template.base import FilterExpression, kwarg_re, TemplateSyntaxError
  from django.template.loader import get_template
  ...
  </code></pre>