[CentralOH] dict.setdefault() returns a reference

[jep200404 at columbus.rr.com]

On Tue, 10 Mar 2015 21:47:38 -0400, jep200404 at columbus.rr.com wrote:

>             hourdict = hoursdict.setdefault(hour, {})
>             hourdict[formula_type] = {}
>             (parser[formula_type])(line, hourdict[formula_type])

That dict.setdefault() returns a reference is significant.
See http://colug.net/python/cohpy/20150310/,
especially cells 11 and 12, but earlier cells also.