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This is really stumping me... Here is the nub of the issue:

if hasattr(sys.stderr, 'fileno'):
    if callable(sys.stderr.fileno):
       i = sys.stderr.fileno()

When this statement executes, the 2 conditions pass, BUT the call to fileno() bombs with an AttributeError!! Don't believe me? Here's the stack dump:

Request Method: GET Request URL:

https://XXXX/YYYY/abcdef/hazards/NSP-F15-22/pdf/

Django Version: 1.8.3 Python Version: 3.4.0 Installed Applications: ('django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.staticfiles', 'django.contrib.sites', 'django.contrib.flatpages', 'crispy_forms', 'wkhtmltopdf', 'ckeditor', ...) Installed Middleware: ('django.contrib.sessions.middleware.SessionMiddleware', 'django.middleware.common.CommonMiddleware', 'django.middleware.csrf.CsrfViewMiddleware', 'django.contrib.auth.middleware.AuthenticationMiddleware', 'django.contrib.auth.middleware.SessionAuthenticationMiddleware', 'django.contrib.messages.middleware.MessageMiddleware', 'django.middleware.clickjacking.XFrameOptionsMiddleware', 'django.middleware.security.SecurityMiddleware', 'django.contrib.flatpages.middleware.FlatpageFallbackMiddleware')

Traceback: File "/usr/local/lib/python3.4/dist-packages/django/core/handlers/base.py" in get_response 164. response = response.render() File "/usr/local/lib/python3.4/dist-packages/django/template/response.py" in render 158. self.content = self.rendered_content File "/usr/local/lib/python3.4/dist-packages/wkhtmltopdf/views.py" in rendered_content 148.footer_filename=footer_filename) File "/usr/local/lib/python3.4/dist-packages/wkhtmltopdf/views.py" in convert_to_pdf 107. return wkhtmltopdf(pages=[filename], **cmd_options) File "/usr/local/lib/python3.4/dist-packages/wkhtmltopdf/utils.py" in wkhtmltopdf

101. i = sys.stderr.fileno()

Exception Type: AttributeError at /abcdef/hazards/NSP-F15-22/pdf/

Exception Value: 'mod_wsgi.Log' object has no attribute 'fileno'

This all runs fine in our development environment running django dev server (i.e., not using wsgi). But in our production env. we are serving a Django app on apache with mod_wsgi on Ubuntu. All software latest stable versions (Ubuntu 14.04, python 3.4, django 1.8, libapache2-mod-wsgi-py3 3.4-4ubuntu2.1.14.04.2) .

The issue seems to stem from wsgi replacing sys.stderr with a mod_wsgi.Log object. Back in 2013 a patch was added in django-wkhtml2pdf to fix this issue... see: https://github.com/incuna/django-wkhtmltopdf/pull/40

Unfortunately, as you can see from the code that is bombing on me, sys.stderr does have a 'fileno' attribute AND the fileno attribute is callable, BUT when you go to call it, Python raises the AttributeError exception shown above.

I'm at wits end - must be missing something really stupid here. Would be ever so grateful for any hints on what might be the cause or where to look next.

powderflask
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  • According to python docs (https://docs.python.org/2/library/functions.html#callable), "... If this returns true, it is still possible that a call fails..." – user590028 Jul 28 '15 at 19:54
  • The only explanation I can think of is that `type(sys.stderr)` is an extension class (i.e. implemented in C instead of Python) which raises an AttributeError when you call its `fileno()` method. Maybe it's trying to proxy to some other object (perhaps a mod_wsgi.Log instance) in a really strange/broken way? I'd try to reduce this to a minimal test case and report a bug in Django. – Kevin Jul 28 '15 at 20:04
  • Thanks for the tips - I'll try to reduce the test case. – powderflask Jul 28 '15 at 21:53
  • You are using an ancient mod_wsgi version. Upgrading mod_wsgi would be a good start to see if the issue exists in latest versions. I can't replicate the problem. – Graham Dumpleton Jul 28 '15 at 22:39
  • OK - I narrowed it down to a simple test case: https://github.com/GrahamDumpleton/mod_wsgi/issues/85 I will install the most recent code from your github repository and see if I can replicate it - thanks for replying Graham - awesome! – powderflask Jul 28 '15 at 23:01
  • running now with mod_wsgi 4.4.13 - test case still failing. See: https://github.com/GrahamDumpleton/mod_wsgi/issues/85 – powderflask Jul 28 '15 at 23:46

1 Answers1

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This issue appears to be caused by by python 3 or an incompatibility with python 3. Bug report currently in queue at https://github.com/GrahamDumpleton/mod_wsgi/issues/85.

Huge shout out to Kevin and Graham for quick and helpful responses. Thank you!

powderflask
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