I started having a similar issue after updating to macOS Mojave 10.14.6.

I'm not using idle, but the following minimal code has a similar issue:
```python
import tkinter as tk

w = tk.Tk()
w.mainloop()
```
The crash happens on `mainloop`.

This worked for me on macOS <= 10.14.5, but started crashing after updating to macOS 10.14.6. I'm using miniconda with conda=4.7.10, python=3.7.3, and tk=8.6.8.

The above code does work fine on the macOS 10.14.6 in a conda environment with python=3.6.2 and tk=8.5.18. But I really want to use python 3.7, which requires tk>=8.6.8, at least on the default conda channels.