Runtime error is raised when iterating tree in Python3.7

[EdwardWooCN]

This error occurs in function iter_slice(self, slice: slice) -> Iterator[Record].
Since python 3.5, when StopIteration is raised inside a generator, it is replaced with RuntimeError. The alternative is return. (See in https://www.python.org/dev/peps/pep-0479/)
I have verified this change.

[NicolasLM]

Hi, makes sense. Would you mind sending a PR?

[EdwardWooCN]

I have just checked the code in github, it is already fixed 3 years ago by you. But it is not fixed in the pip package(version 0.0.3).

[NicolasLM]

Right, I should make a release to PyPI.