How about following the [numpy docstring standard](https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt) suggestion and common practice in numpy / scipy docstrings?

> When a parameter can only assume one of a fixed set of values, those values can be listed in braces, with the default appearing first:
```
order : {'C', 'F', 'A'}
    Description of `order`.
```

(there's probably other places where this should be changed.)