get function of TraitType(BaseDescriptor) is called right after start ipython and then run forever?

Hi, I'm using ipython and trailets. I met a bug in my code and eventually lead me to try to print something inside `get` function of `TraitType(BaseDescriptor)`.

I put `print('enter get function')` before `try` block [here](https://github.com/ipython/traitlets/blob/master/traitlets/traitlets.py#L518). I observed that once I start `ipython`, `enter get function` started printing out and never stopped. It looks like `get` was called in a loop and run forever. Is there something that could help me understand this?

output
```
enter get function
enter get function
enter get function
enter get function
enter get function
...
```

Below are version info:
ipython 7.7.0
python 3.7
traitlets 4.3.3