🐍 Be more lenient when accepting args to file I/O

[thorstenhater]

PyArbor I/O routines now try to cast filename arguments to a string.
This allows passing pathlib.Path objects.

Example

here = Path(__file__).parent
cat = A.load_catalogue(here / 'local-catalogue.so')

[bcumming]

One small suggestion to improve robustness.

[bcumming]

Here we are using the py::object as though it can be converted to a std::string, without checking.

The errors when a type that can't be converted to string, or converts to an odd string, is passed.

How about writing a little helper function that tests the type and converts it to a string, or throws an exception with a helpful message?

[thorstenhater]

I thought you might bring up this argument. Essentially we are calling foo.__str__ here, which is essentially in line with Python's behaviour. We have two options:

1. Restrict to a known good set of py-types (String, Path, ...) trying each in turn
2. Accept all the odd things that can happen when calling eg arbor.load_swc(42)

I tend to option 1 as well, but wanted to have a neutral verdict first.

[bcumming]

... option 1!

[brenthuisman]

The Pythonic way is to try and handle errors (which can just be "Unknown input provided, aborting...").

[thorstenhater]

Actually, we should be taking FileHandles, including StringIO. But that is probably not possible.

[brenthuisman]

I'd be happy to have a new-style typed error here, but I'll leave that up to you.

[thorstenhater]

That's a good point, I should remember my own demands.