[Python-modules-team] Bug#888603: python3-paste: errormiddleware fails with write() argument must be str, not bytes when exception trapped

[Alternative admin]

Package: python3-paste
Version: 2.0.3+dfsg-4
Severity: important

Dear Maintainer,

I am using Paste's ErrorMiddleware to trap exceptions in a WSGI based
app. running under Apache mod_wsgi   eg

from paste.exceptions.errormiddleware import ErrorMiddleware
.....
application = ErrorMiddleware(application, debug=True)

With this in place normal use of my application is fine.  However, if my
application throws an exception, instead of the expected diagnostic
screen I get a 500 - Server error.

The Apache error log shows 

AssertionError

During handling of the above exception, another exception occurred:
  
Traceback (most recent call last):
  File
   "/usr/lib/python3/dist-packages/paste/exceptions/errormiddleware.py",
  line 154, in __call__
  response = self.exception_handler(exc_info, environ)
  File
   "/usr/lib/python3/dist-packages/paste/exceptions/errormiddleware.py",
  line 188, in exception_handler
   simple_html_error=simple_html_error)
  File
   "/usr/lib/python3/dist-packages/paste/exceptions/errormiddleware.py",
   line 391, in handle_exception
    error_stream.write(line)
   TypeError: write() argument must be str, not bytes

The firstline above is the error forced in my app, the rest is in the
middeware.

I have found another report of this on the Internet but no solution - 
  https://stackoverflow.com/questions/44792287/why-does-paste-errormiddleware-throw-an-exception-when-i-use-it-with-my-python-3

Regards

Tony Middleton

-- System Information:
Debian Release: 9.3
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-5-amd64 (SMP w/1 CPU core)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages python3-paste depends on:
ii  python3                3.5.3-1
ii  python3-pkg-resources  33.1.1-1
ii  python3-six            1.10.0-3
ii  python3-tempita        0.5.2-2

Versions of packages python3-paste recommends:
ii  libjs-mochikit   1.4.2-4
ii  python3-openssl  16.2.0-1

Versions of packages python3-paste suggests:
pn  libapache2-mod-python                 <none>
pn  libapache2-mod-scgi                   <none>
ii  libapache2-mod-wsgi-py3 [httpd-wsgi]  4.5.11-1
pn  python3-pastedeploy                   <none>

-- no debconf information