Python 3.7.0 No module named 'PyQt5.QtWebEngineWidgets'

Just install PyQtWebEngine

pip install PyQtWebEngine

If you still got problems with PyQt, try uninstalling all of the PyQt related libraries:

pip uninstall PyQt5
pip uninstall PyQt5-sip
pip uninstall PyQtWebEngine

Then install them again as bellow - 

pip install PyQt5
pip install PyQt5-sip
pip install PyQtWebEngine

which should fix the following errors:

ModuleNotFoundError: No module named 'PyQt5.sip'
ModuleNotFoundError: No module named 'PyQt5.QtWebEngineWidgets'

If you still got problems uninstalling the libraries, go to your Python folder, like:

C:\Users\<USERNAME>\AppData\Local\Programs\Python\Python<PYTHON-VERSION>\Lib\site-packages

and manually delete the PyQt folders, then uninstall everything and install again. Make sure you have the latest Python version and have upgraded your pip too.

# install latest python version for your operating system, then
# upgrade pip:
pip install --upgrade pip

# uninstall everything
pip uninstall PyQt5
pip uninstall PyQt5-sip
pip uninstall PyQtWebEngine

# install everything
pip install PyQt5
pip install PyQt5-sip
pip install PyQtWebEngine

This will solve the error.