gufe objects not giving informative signatures

[dwhswenson]

Our objects are not returning useful signatures. They all return a <Signature (*args, **kwargs)>.

This is annoying when using our objects in IDEs, e.g., using shift-tab for quick help in Jupyter.

Expected behavior would be to see the actual signature coming from the __init__.

I suspect the source of this problem is our metaclass. Specifically, I think we're actually seeing the signature from _GufeTokenizableMeta.__call__. Not an urgent issue, but I wanted to document it since I'm pretty sure I've identified the reason, although I don't have a trivial solution.

In [1]: import inspect

In [2]: import gufe
LICENSE: Could not open license file "oe_license.txt" in local directory
LICENSE: N.B. OE_LICENSE environment variable is not set
LICENSE: N.B. OE_DIR environment variable is not set
LICENSE: No product keys!
LICENSE: No product keys!
LICENSE: No product keys!
LICENSE: No product keys!
g
In [3]: gufe.__version__
Out[3]: 'v0.2.post227+g69ad4d2'

In [4]: inspect.signature(gufe.ChemicalSystem)
Out[4]: <Signature (*args, **kwargs)>

In [5]: inspect.signature(gufe.SmallMoleculeComponent)
Out[5]: <Signature (*args, **kwargs)>

In [6]: inspect.signature(gufe.ProteinComponent)
Out[6]: <Signature (*args, **kwargs)>

In [7]: inspect.signature(inspect.Signature)
Out[7]: <Signature (parameters=None, *, return_annotation, __validate_parameters__=True)>

[dwhswenson]

Of course, someone has asked on SO: https://stackoverflow.com/questions/49740290/call-from-metaclass-shadows-signature-of-init

Looks like we need to modify the __signature__ attribute per PEP 362.

[dwhswenson]

Fixed in #216.