[issue20630] Add sorting helpers for collections containing None values

[Raymond Hettinger]

Raymond Hettinger added the comment:

> If it is in fact specific to sorting, then this specific symptom
> and "the problem" are in fact the same thing ;-)

The first rule of tautology club is the first rule of tautology club ;-)

FWIW, we had to add a work-around for this in pprint._safe_key class.  Without that work-around, it was difficult to work with JSON-style data hierarchies:

# wouldn't pprint() without the _safe_key() work-around:
temperatures = {'Jan': 25.2, 'Feb': 22.3, 'Mar': None, 'Apr': 19.1,
                'May': 22.2, 'Jun': None, 'July': 22.3}

I think this will be typical for the kind of issue people will encounter when using None as a placeholder for missing data.

FWIW, if None stays non-comparable, Nick's additions look fine to me.  I just think it easier for everyone to restore None's universal comparability rather than adding work-arounds for the problems caused by removing that capability.

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<http://bugs.python.org/issue20630>
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