Idle3 (of python3) regularly crashes when in a window and using the middle mousewheel.
There is always the same error left in Terminal:

Traceback (most recent call last):   File "/usr/local/bin/idle3", line 5, in   main()   File
  "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/idlelib/pyshell.py",
  line 1548, in main
      root.mainloop()   File
  "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/tkinter/init.py", line 1280, in mainloop  self.tk.mainloop(n)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xFF in position 0: invalid continuation byte
  `
The problem seems to be that brew installed python without tcl-tk, thus using the old tcl-tk from mac-os. This one has a problem interpreting some mousewheel commands.
The solution  : 
brew reinstall python --with-tcl-tk
My Idle (idle3) from python installed with homebrew on a mac crashes