Importing "Iterable" needs updating for Python > 3.9

[nbrunett]

I was trying to run pycprops in Python 3.10.2 (which uses astrodendro) and encountered the following import error (partial traceback to exclude my scripts and directory names):

File ".../astrodendro/__init__.py", line 3
    from .dendrogram import Dendrogram, periodic_neighbours
File ".../astrodendro/dendrogram.py", line 8
    from collections import Iterable
ImportError: cannot import name 'Iterable' from 'collections'

It looks like importing Iterable from collections has changed after Python 3.9 (see text below the first table at the top of the page here).

Changing line 8 in dendrogram.py from

from collections import Iterable

to

try:
    # Python <= 3.9
    from collections import Iterable
except ImportError:
    # Python > 3.9
    from collections.abc import Iterable

eliminated the problem for me (inspired by suggestion in the comment here).

Let me know if you need any more information.

[keflavich]

could you please submit this as a pull request? It looks like you've found the solution so you should get credit for the change