Fix E731 error for sorters.py

[stevenhua0320]

No description provided.

[sbillinge]

please see my inline comments and try and update all the functions using this as a template.

[sbillinge]

let's give this a more intuitive name like document

then in the numpy-style docstring it would look like

document:  dict
  the document that is expected to contain date-like information in "year" and/or "month"

[sbillinge]

we need a blank line here in all the docstrings, and the first line inline, so something like:

"""Convert a Datetime object of the doc to a float key.

Parameters
------------

[sbillinge]

I think there is no key here, maybe more descriptive would be the float serialization of the date information in the document

[sbillinge]

sorry for this, but please see my edited comment. I read the code more carefully and I realize that the thing I called "date" is not a date but is a document, so let's call it a document. My suggested docstring is in the edited comment.

[sbillinge]

please see additional comments inline.

[sbillinge]

this should be "end_year" and "end_month"

[sbillinge]

I think the input should again be called document here.

[sbillinge]

this is not a serialization, it is just returning the category item. We probably don't need this function in fact. Like elsewhere, we could just put the lambda inside the sorter, unless it is used in many places. For now, just make changes to the docstring and let's go with that.