add __str__() and _repr_html_() methods for the Graph, Epoch, et al.

[grahamgower]

So that we do better than, e.g.:

Graph(description='asymmetric migration between two extant demes', time_units='generations', generation_time=None, doi=[], demes=[Deme(id='X', description=None, start_time=inf, ancestors=[], proportions=[], epochs=[Epoch(start_time=inf, end_time=1000, start_size=5000, end_size=5000, size_function='constant', selfing_rate=0, cloning_rate=0)]), Deme(id='A', description=None, start_time=1000, ancestors=['X'], proportions=[1.0], epochs=[Epoch(start_time=1000, end_time=0, start_size=5000, end_size=5000, size_function='constant', selfing_rate=0, cloning_rate=0)]), Deme(id='B', description=None, start_time=1000, ancestors=['X'], proportions=[1.0], epochs=[Epoch(start_time=1000, end_time=0, start_size=5000, end_size=5000, size_function='constant', selfing_rate=0, cloning_rate=0)])], migrations=[AsymmetricMigration(start_time=1000, end_time=0, rate=0.0001, source='A', dest='B')], pulses=[])

Like recently added to msprime's Demography class.

[jeromekelleher]

I'm really missing a proper str implementation when working with demes - any thoughts on what this should look like? Even a simple tabular output would be very helpful.

[grahamgower]

The attrs default leaves a lot to be desired. There's an example here using the prettyprinter package which looks nice: python-attrs/attrs#508 (comment)

[jeromekelleher]

I think I'd be better to just hand craft something - it's time well spent, as it makes debugging so much easier.

[grahamgower]

Well, we're making the claim that the yaml files are human readable, so how about using that?

>>> import demes
>>> demes.Graph.__repr__ = demes.dumps
>>> demes.load("examples/gutenkunst_ooa.yml")
description: The Gutenkunst et al. (2009) OOA model.
time_units: years
generation_time: 25
doi:
- https://doi.org/10.1371/journal.pgen.1000695
demes:
- name: ancestral
  description: Equilibrium/root population
  epochs:
  - end_time: 220000.0
    start_size: 7300
- name: AMH
...

[jeromekelleher]

Excellent point! Yes, that's clearly the right approach.

[grahamgower]

It turns out that it's possible to output a mix of flow style and block style using ruamel.yaml. I haven't quite figured out the incantation to do so, but if we can output deme ancestors/proportions and epochs/migrations/pulses using the flow style, this will certainly make for compact and readable debug output.