TypeError: a bytes-like object is required, not 'str'

[frapell]

When on Python 3 with Zope 5.1 or 5.2 (This issue is fixed on Zope 5.3 and up), you get

Traceback (innermost last):
  Module ZPublisher.WSGIPublisher, line 167, in transaction_pubevents
  Module ZPublisher.WSGIPublisher, line 376, in publish_module
  Module ZPublisher.WSGIPublisher, line 271, in publish
  Module ZPublisher.mapply, line 85, in mapply
  Module ZPublisher.WSGIPublisher, line 68, in call_object
  Module plone.app.theming.browser.controlpanel, line 73, in __call__
  Module plone.app.theming.browser.controlpanel, line 191, in update
TypeError: a bytes-like object is required, not 'str'

When trying to save custom styles from /@@theming-controlpanel -> Advanced Settings -> Custom Styles

To reproduce:

1. Have a Plone 5 instance with Python 3, using Zope 5.1 or 5.2
2. Visit /@@theming-controlpanel and add some Parameter expressions under Advanced settings -> Theme details, for instance

url = context/absolute_url
portal_url = portal_state/portal_url

3. Go to Custom Styles and try to save some custom CSS, for instance

body{
color:red;
}

4. Click Save

[mauritsvanrees]

I can have a look later. But one thing jumps out:

Have a Plone 5 instance with Python 3, using Zope 5.1 or 5.2

This is not supported. Plone 5 only works with Zope 4. Or at least it is only tested with Zope 4. I would not recommend using a higher Zope version.

[frapell]

Yeah... I don't quite remember why we went to Zope 5 honestly... But we haven't had any issues (except this :P) Is there any specific concern it comes to your mind about it?