Some WinPython users need to replace PyQt5 with PyQt4. In my case, because of this bug: matplotlib/matplotlib#7688

Here is the procedure that worked for me with 64-bit WinPython 3.5.2.4Qt5b3:

1. Download from http://www.lfd.uci.edu/~gohlke/pythonlibs/#pyqt4
2. Copy file to D:\toto\PyQt4‑4.11.4‑cp35‑none‑win_amd64.whl
3. Run "WinPython Command Prompt.exe" as administrator
4. In the cmd.exe window, type >wppm -u PyQt5
5. In the cmd.exe window, type >wppm -i D:\toto\PyQt4‑4.11.4‑cp35‑none‑win_amd64.whl
6. Delete the folder "%WINPYDIR%\Lib\site-packages\PyQt5"

Step 6) is necessary because wppm does not delete the folder with the uninstall of PyQt5, and many WinPython scripts (such as env.bat) look for the existence of the folder "%WINPYDIR%\Lib\site-packages\PyQt5" to determine if Qt5 is used.

Should wppm be changed so that step 6) is not necessary?