Installing qgis2web in qgis3 (2.99) on ubuntu 16.04

Question

When installing the plugin qgis2web through the plugin manager on the qgis 2.99 nightly release I get the following error message. Does anyone know what I need to do to get it working. I've not seen an obvious corresponding issue on the github repo.

Couldn't load plugin 'qgis2web' due to an error when calling its classFactory() method 

ImportError: No module named 'PyQt5.QtWebKitWidgets' 
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/qgis/utils.py", line 336, in startPlugin
    plugins[packageName] = package.classFactory(iface)
  File "/home/will/.local/share/QGIS/QGIS3/profiles/default/python/plugins/qgis2web/__init__.py", line 28, in classFactory
    from .qgis2web import Qgis2Web
  File "/usr/lib/python3/dist-packages/qgis/utils.py", line 664, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "/home/will/.local/share/QGIS/QGIS3/profiles/default/python/plugins/qgis2web/qgis2web.py", line 30, in 
    from qgis2web.maindialog import MainDialog
  File "/usr/lib/python3/dist-packages/qgis/utils.py", line 664, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "/home/will/.local/share/QGIS/QGIS3/profiles/default/python/plugins/qgis2web/maindialog.py", line 55, in 
    from qgis.PyQt.QtWebKitWidgets import QWebView, QWebInspector, QWebPage
  File "/usr/lib/python3/dist-packages/qgis/utils.py", line 664, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "/usr/lib/python3/dist-packages/qgis/PyQt/QtWebKitWidgets.py", line 26, in 
    from PyQt5.QtWebKitWidgets import *
  File "/usr/lib/python3/dist-packages/qgis/utils.py", line 664, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
ImportError: No module named 'PyQt5.QtWebKitWidgets'


Python version: 3.5.2 (default, Nov 23 2017, 16:37:01) [GCC 5.4.0 20160609] 
QGIS version: 2.99.0-Master Master, 585a4d3 

Python Path:
/home/will/.local/share/QGIS/QGIS3/profiles/default/python/plugins/gml_application_schema_toolbox/extlibs
/usr/share/qgis/python
/home/will/.local/share/QGIS/QGIS3/profiles/default/python
/home/will/.local/share/QGIS/QGIS3/profiles/default/python/plugins
/usr/share/qgis/python/plugins
/usr/lib/python35.zip
/usr/lib/python3.5
/usr/lib/python3.5/plat-x86_64-linux-gnu
/usr/lib/python3.5/lib-dynload
/home/will/.local/lib/python3.5/site-packages
/usr/local/lib/python3.5/dist-packages
/usr/lib/python3/dist-packages
/home/will/.local/share/QGIS/QGIS3/profiles/default/python

Answer 1

The missing module is 'PyQt5.QtWebKitWidgets' which can be installed on ubuntu as part of the 'python3-pyqt5.qtwebkit' deb package.

To check if it is already installed, and ensure it is available, the command is:

apt-cache policy python3-pyqt5.qtwebkit

Assuming it isn't installed, then it can be installed with:

sudo apt install python3-pyqt5.qtwebkit

@TomChadwin put me on the right track.

Answer 2

I don't know what distribution you are on, but this is likely to be the availability of QtWebkit, or its Python bindings. See if you can ensure they are installed.