Just to be sure, I have deleted all the packages installed for python3.6 and ran sudo pip3 install joulescope_ui again to start clean.
Collecting joulescope_ui
Collecting pyqtgraph@ https://github.com/jetperch/pyqtgraph/tarball/c8548b3246d29ee84a1ef76ebf63a5bb0e39c917#egg=pyqtgraph-0.11.0.dev0requests>=2.0.0 (from joulescope_ui)
Collecting joulescope>=0.4.5 (from joulescope_ui)
Collecting python-dateutil>=2.7.3 (from joulescope_ui)
Downloading https://files.pythonhosted.org/packages/41/17/c62faccbfbd163c7f57f3844689e3a78bae1f403648a6afb1d0866d87fbb/python_dateutil-2.8.0-py2.py3-none-any.whl (226kB)
100% |████████████████████████████████| 235kB 1.0MB/s
Collecting pyside2>=-5.11.2 (from joulescope_ui)
Downloading https://files.pythonhosted.org/packages/3d/a1/9300c616621ba1d1a3426d98b59cd5403045eafaa0263e68e7d4d48a49e4/PySide2-5.13.0-5.13.0-cp35.cp36.cp37-abi3-manylinux1_x86_64.whl (152.9MB)
100% |████████████████████████████████| 152.9MB 12kB/s
Collecting numpy>=1.15.2 (from joulescope_ui)
Downloading https://files.pythonhosted.org/packages/87/2d/e4656149cbadd3a8a0369fcd1a9c7d61cc7b87b3903b85389c70c989a696/numpy-1.16.4-cp36-cp36m-manylinux1_x86_64.whl (17.3MB)
100% |████████████████████████████████| 17.3MB 108kB/s
Collecting json5>=0.6.1 (from joulescope_ui)
Downloading https://files.pythonhosted.org/packages/30/44/062543d4a6718f99d82e5ecf9140dbdee8a03122f2c34fbd0b0609891707/json5-0.8.5-py2.py3-none-any.whl
Collecting pymonocypher>=0.1.0 (from joulescope>=0.4.5->joulescope_ui)
Requirement already satisfied (use --upgrade to upgrade): six>=1.5 in /usr/lib/python3/dist-packages (from python-dateutil>=2.7.3->joulescope_ui)
Collecting shiboken2==5.13.0 (from pyside2>=-5.11.2->joulescope_ui)
Downloading https://files.pythonhosted.org/packages/d5/e2/e121fa55a759a286588a4017f57f34c03e8b35722131a2189a4f0e84bbac/shiboken2-5.13.0-5.13.0-cp35.cp36.cp37-abi3-manylinux1_x86_64.whl (792kB)
100% |████████████████████████████████| 798kB 451kB/s
Installing collected packages: numpy, pyqtgraph, python-dateutil, pymonocypher, joulescope, shiboken2, pyside2, json5, joulescope-ui
Found existing installation: numpy 1.11.0
Not uninstalling numpy at /usr/lib/python3/dist-packages, outside environment /usr
Found existing installation: python-dateutil 2.4.2
Not uninstalling python-dateutil at /usr/lib/python3/dist-packages, outside environment /usr
Successfully installed joulescope-0.4.5 joulescope-ui-0.4.5 json5-0.8.5 numpy-1.16.4 pymonocypher-0.1.2 pyqtgraph-0.10.0 pyside2-5.13.0 python-dateutil-2.8.0 shiboken2-5.13.0
After this I get the same: cannot import name ‘QtGui’