text: Q:
  
  Unable to launch ReText installed with pip3 - how to fix?
  
  I'm running Ubuntu 16.04.5 LTS.
  Previously I have installed ReText editor from official repository (version 5.3.1-1).
  I removed this version with:
  sudo apt-get purge retext
  sudo apt-get autoremove
  
  Now I want to get latest version from pip3:
  sudo apt install python3-pip
  sudo pip3 install ReText
  
  Installation ended successfully. But if try to launch ReText from terminal with retext - I get:
  $ retext 
  Traceback (most recent call last):
    File "/usr/local/bin/retext", line 26, in <module>
      from ReText import datadirs, settings, globalSettings, app_version
    File "/usr/local/lib/python3.5/dist-packages/ReText/__init__.py", line 24, in <module>
      from PyQt5.QtCore import QByteArray, QLocale, QSettings, QStandardPaths
  ImportError: /usr/local/lib/python3.5/dist-packages/PyQt5/QtCore.so: undefined symbol: PySlice_AdjustIndices
  
  How to fix this problem?
  
  System info:
  $ pip3 --version
  pip 18.0 from /usr/local/lib/python3.5/dist-packages/pip (python 3.5)
  
  $ python3 --version
  Python 3.5.2
  
  $ which python3
  /usr/bin/python3
  
  $ dpkg -S /usr/bin/python3
  python3-minimal: /usr/bin/python3
  
  $ pip3 list --user
  
  $ pip3 list
  Package                      Version               
  ---------------------------- ----------------------
  alabaster                    0.7.11                
  apparmor                     2.10.95               
  apparmor.click               0.3.13.1              
  apt-xapian-index             0.47                  
  apturl                       0.5.2                 
  argcomplete                  1.9.4                 
  asn1crypto                   0.24.0                
  astroid                      2.0.4                 
  Babel                        2.6.0                 
  backcall                     0.1.0                 
  beautifulsoup4               4.6.3                 
  bleach                       2.1.4                 
  Brlapi                       0.6.4                 
  cairocffi                    0.9.0                 
  certifi                      2018.8.24             
  cffi                         1.11.5                
  chardet                      3.0.4                 
  checkbox-ng                  1.0.0                 
  checkbox-support             0.38.0                
  click                        6.7                   
  cloudpickle                  0.5.6                 
  command-not-found            0.3                   
  cryptography                 2.3.1                 
  cycler                       0.10.0                
  decorator                    4.3.0                 
  defer                        1.0.6                 
  defusedxml                   0.5.0                 
  devscripts                   1.0.0                 
  docutils                     0.14                  
  ecdsa                        0.13                  
  entrypoints                  0.2.3                 
  esptool                      2.5.0                 
  guacamole                    0.9.2                 
  html5lib                     1.0.1                 
  idna                         2.7                   
  imagesize                    1.1.0                 
  indicator-cpufreq            0.2.2                 
  ipykernel                    4.9.0                 
  ipython                      6.5.0                 
  ipython-genutils             0.2.0                 
  isort                        4.3.4                 
  jedi                         0.12.1                
  jeepney                      0.3.1                 
  Jinja2                       2.10                  
  jsonschema                   2.6.0                 
  jupyter-client               5.2.3                 
  jupyter-core                 4.4.0                 
  keyring                      15.1.0                
  kiwisolver                   1.0.1                 
  language-selector            0.1                   
  lazy-object-proxy            1.3.1                 
  LibAppArmor                  2.10.95               
  lightdm-gtk-greeter-settings 1.2.1                 
  louis                        2.6.4                 
  lxml                         4.2.5                 
  Magic-file-extensions        0.2                   
  Mako                         1.0.7                 
  Markdown                     2.6.11                
  Markups                      3.0.0                 
  MarkupSafe                   1.0                   
  mate-tweak                   3.5.10                
  matplotlib                   2.2.3                 
  mccabe                       0.6.1                 
  mistune                      0.8.3                 
  nbconvert                    5.4.0                 
  nbformat                     4.4.0                 
  nose                         1.3.7                 
  notify2                      0.3.1                 
  numexpr                      2.6.8                 
  numpy                        1.15.1                
  numpydoc                     0.8.0                 
  onboard                      1.2.0                 
  packaging                    17.1                  
  padme                        1.1.1                 
  pandas                       0.23.4                
  pandocfilters                1.4.2                 
  parso                        0.3.1                 
  pep8                         1.7.1                 
  pexpect                      4.6.0                 
  pickleshare                  0.7.4                 
  Pillow                       5.2.0                 
  pip                          18.0                  
  plainbox                     0.38.0                
  ply                          3.11                  
  progressbar                  2.5                   
  prompt-toolkit               2.0.4                 
  psutil                       5.4.7                 
  ptyprocess                   0.6.0                 
  pyaes                        1.6.1                 
  pyasn1                       0.4.4                 
  pycairo                      1.17.1                
  pycodestyle                  2.4.0                 
  pycparser                    2.18                  
  pycrypto                     2.6.1                 
  pycups                       1.9.73                
  pycurl                       7.43.0.2              
  pyflakes                     2.0.0                 
  Pygments                     2.2.0                 
  PyGObject                    3.30.1                
  pylint                       2.1.1                 
  PyOpenGL                     3.1.0                 
  pyparsing                    2.2.0                 
  PyQt5                        5.11.2                
  PyQt5-sip                    4.19.12               
  pyserial                     3.4                   
  python-apt                   1.1.0b1+ubuntu0.16.4.2
  python-dateutil              2.7.3                 
  python-dbusmock              0.18                  
  python-debian                0.1.33                
  python-gnupg                 0.4.3                 
  python-markdown-math         0.6                   
  python-systemd               231                   
  pytz                         2018.5                
  pyxdg                        0.26                  
  PyYAML                       3.13                  
  pyzmq                        17.1.2                
  QtAwesome                    0.4.4                 
  qtconsole                    4.4.1                 
  QtPy                         1.5.0                 
  reportlab                    3.5.6                 
  requests                     2.19.1                
  requests-unixsocket          0.1.5                 
  ReText                       7.0.3                 
  roman                        3.0                   
  rope                         0.11.0                
  scipy                        1.1.0                 
  screen-resolution-extra      0.0.0                 
  SecretStorage                3.1.0                 
  selenium                     3.14.0                
  sessioninstaller             0.0.0                 
  setuptools                   40.3.0                
  simplegeneric                0.8.1                 
  sip                          4.19.8                
  six                          1.11.0                
  snowballstemmer              1.2.1                 
  Sphinx                       1.8.0                 
  sphinx-rtd-theme             0.4.1                 
  sphinxcontrib-websupport     1.1.0                 
  spyder                       3.3.1                 
  spyder-kernels               1.1.0                 
  ssh-import-id                5.6                   
  system-service               0.3                   
  tables                       3.4.4                 
  testpath                     0.3.1                 
  tornado                      5.1.1                 
  traitlets                    4.3.2                 
  typed-ast                    1.1.0                 
  ubuntu-drivers-common        0.0.0                 
  Ubuntu-Make                  18.5                  
  ufw                          0.35                  
  urllib3                      1.23                  
  urwid                        2.0.1                 
  usb-creator                  0.3.0                 
  wcwidth                      0.1.7                 
  webencodings                 0.5.1                 
  wheel                        0.31.1                
  wrapt                        1.10.11               
  xcffib                       0.6.0                 
  xdiagnose                    3.8.4.1               
  xkit                         0.0.0                 
  XlsxWriter                   1.1.0  
  
  $ dpkg -l | grep python3- | grep ^ii | awk '{print $2}'
  ipython3-qtconsole
  libpython3-all-dev:amd64
  libpython3-dev:amd64
  libpython3-stdlib:amd64
  python3-alabaster
  python3-all
  python3-all-dev
  python3-apparmor
  python3-apparmor-click
  python3-apport
  python3-apt
  python3-aptdaemon
  python3-aptdaemon.gtk3widgets
  python3-aptdaemon.pkcompat
  python3-argcomplete
  python3-babel
  python3-brlapi
  python3-bs4
  python3-cairo
  python3-cairocffi
  python3-cffi
  python3-cffi-backend
  python3-chardet
  python3-checkbox-ng
  python3-checkbox-support
  python3-click-package
  python3-commandnotfound
  python3-cups
  python3-cupshelpers
  python3-cycler
  python3-dateutil
  python3-dbus
  python3-dbus.mainloop.qt
  python3-dbusmock
  python3-debian
  python3-decorator
  python3-defer
  python3-dev
  python3-distupgrade
  python3-docutils
  python3-gdbm:amd64
  python3-gi
  python3-gi-cairo
  python3-gnupg
  python3-gst-1.0
  python3-guacamole
  python3-html5lib
  python3-jedi
  python3-jinja2
  python3-libapparmor
  python3-louis
  python3-lxml
  python3-magic
  python3-mako
  python3-markupsafe
  python3-matplotlib
  python3-minimal
  python3-newt
  python3-nose
  python3-notify2
  python3-numexpr
  python3-numpy
  python3-packagekit
  python3-padme
  python3-pandas
  python3-pandas-lib
  python3-pep8
  python3-pexpect
  python3-pil:amd64
  python3-pip
  python3-pkg-resources
  python3-plainbox
  python3-ply
  python3-problem-report
  python3-progressbar
  python3-psutil
  python3-ptyprocess
  python3-pyasn1
  python3-pyatspi
  python3-pycparser
  python3-pycurl
  python3-pyflakes
  python3-pygments
  python3-pyparsing
  python3-pyqt4
  python3-pyqt5
  python3-pyqt5.qtsvg
  python3-pyqt5.qtwebkit
  python3-renderpm:amd64
  python3-reportlab
  python3-reportlab-accel:amd64
  python3-requests
  python3-roman
  python3-scipy
  python3-selenium
  python3-setuptools
  python3-simplegeneric
  python3-sip
  python3-six
  python3-software-properties
  python3-speechd
  python3-sphinx
  python3-sphinx-rtd-theme
  python3-systemd
  python3-tables
  python3-tables-lib
  python3-tk
  python3-tz
  python3-uno
  python3-update-manager
  python3-urllib3
  python3-wheel
  python3-xapian1.3
  python3-xcffib
  python3-xdg
  python3-xkit
  python3-xlsxwriter
  python3-yaml
  python3-zmq
  
  $ dpkg -S /usr/lib/python3/dist-packages | sed 's/, /\n/g'
  python3-libapparmor
  python3-aptdaemon.pkcompat
  python3-aptdaemon
  ubuntu-system-service
  python3-cairo
  python3-bs4
  python3-apparmor-click
  python3-renderpm:amd64
  python3-pyqt5.qtsvg
  python3-pycparser
  python3-pyatspi
  python3-pyasn1
  python3-progressbar
  python3-problem-report
  python3-pexpect
  python3-numexpr
  python3-matplotlib
  python3-packagekit
  python3-numpy
  python3-nose
  python3-jedi
  python3-gst-1.0
  python3-decorator
  python3-cups
  python3-checkbox-support
  python3-checkbox-ng
  python3-plainbox
  python3-chardet
  python3-cairocffi
  language-selector-gnome
  ufw
  python3-distupgrade
  python3-dbus
  python3-update-manager
  python3-gi
  python3-tables-lib
  python3-setuptools
  python3-roman
  python3-requests
  python3-reportlab
  python3-pyqt5
  python3-sip
  python3-sphinx-rtd-theme
  python3-sphinx
  software-properties-common
  python3-selenium
  python3-reportlab-accel:amd64
  python3-pyqt4
  python3-pygments
  python3-pyflakes
  python3-pycurl
  python3-pkg-resources
  python3-pep8
  python3-pandas-lib
  python3-ply
  python3-pil:amd64
  python3-ptyprocess
  python3-pandas
  python3-padme
  python3-notify2
  ssh-import-id
  sessioninstaller
  python3-speechd
  python3-scipy
  python3-newt
  python3-mako
  xdiagnose
  ubuntu-drivers-common
  python3-xapian1.3
  python3-wheel
  python3-urllib3
  python3-tz
  python3-software-properties
  python3-six
  python3-simplegeneric
  python3-pyqt5.qtwebkit
  python3-pyparsing
  python3-psutil
  usb-creator-gtk
  update-manager
  ubuntu-make
  python3-uno
  apturl
  apt-xapian-index
  python3-commandnotfound
  python3-apt
  python3.5
  lsb-release
  language-selector-common
  debconf
  python3-alabaster
  usb-creator-common
  python3-tables
  python3-systemd
  python3-magic
  python3-louis
  python3-defer
  python3-brlapi
  python3-aptdaemon.gtk3widgets
  indicator-cpufreq
  software-properties-kde
  software-properties-gtk
  screen-resolution-extra
  python3-zmq
  python3-yaml
  python3-xlsxwriter
  python3-xkit
  python3-xdg
  python3-xcffib
  python3-markupsafe
  python3-lxml
  python3-jinja2
  python3-dbusmock
  python3-click-package
  python3-html5lib
  python3-guacamole
  python3-gnupg
  python3-gi-cairo
  python3-docutils
  python3-debian
  python3-dbus.mainloop.qt
  python3-dateutil
  python3-cycler
  python3-cupshelpers
  python3-cffi
  python3-cffi-backend
  python3-argcomplete
  gir1.2-unity-5.0:amd64
  devscripts
  blueman
  python3-babel
  gir1.2-ibus-1.0:amd64
  apturl-common
  gnome-orca
  python3-apport
  onboard
  mate-tweak
  lightdm-gtk-greeter-settings
  ipython3-qtconsole
  ipython3
  hplip
  gir1.2-dee-1.0
  python3-pip
  python3-apparmor: /usr/lib/python3/dist-packages
  
  A:
  
  Very strange issue. I have installed ReText with the same method on other Ubuntu 16.04.5 laptop today.  
  The problem was caused by the fact that on first system I have install pip3 some time ago, but on second system I have installed pip3 today. So on the second system pip3 downloaded newest versions of all python-packages.
  On first system I have Spyder installed, it required Qt5 (but lower - pyqt5<5.10 version), so ReText installed and working here without issues.
  The solution is to reinstall Spyder to lower version of Qt5 (5.9.2) python-packages:
  sudo pip3 install spyder
  
  After this ReText works normally:
  
  So I have understood how and why this python dependency hell happens :)
  
  