How to show a dictionary sorted on a value within its data?

Peter Otten __peter__ at
Wed Oct 1 12:24:46 CEST 2014

cl at wrote:

> I have a dictionary as follows:-
> {
> u'StarterAmps1': Row(id=4, ain=u'AIN3', name=u'StarterAmps1',
> conv=6834.374834509803, Description=u'Starter Amps'), u'LeisureVolts':
> Row(id=1, ain=u'AIN0', name=u'LeisureVolts', conv=29.01374215995874,
> Description=u'Leisure Volts'), u'RudderPos': Row(id=6, ain=u'AIN5',
> name=u'RudderPos', conv=0.028125, Description=u'Rudder Position'), u'xx':
> Row(id=7, ain=u'AIN6', name=u'xx', conv=0.028125, Description=u''),
> u'LeisureAmps1': Row(id=3, ain=u'AIN2', name=u'LeisureAmps1',
> conv=32.727273081945, Description=u'Leisure Amps'), u'StarterVolts':
> Row(id=2, ain=u'AIN1', name=u'StarterVolts', conv=28.94469628911757,
> Description=u'Starter Volts') }
> I want to output a menu to a user comprising some parts of the
> dictionary (ain and Description) sorted by ain.
> Is there some incantation of sorted() that will do what I want?  I
> can't quite fathom out the 'key=' parameter needed to sort it by the
> tuple item.  Maybe I need a cmp= ?
> E.g. I want to do something like:-
>     for meas in sorted(adc.cfg, key=???):
>         print(adc.cfg[meas].ain, adc.cfg[meas].Description)
> What's needed in the ???

for meas in sorted(adc.cfg, key=lambda key: adc.cfg[key].ain):
    print(adc.cfg[meas].ain, adc.cfg[meas].Description)

or simpler

for row in sorted(adc.cfg.values(), key=operator.attrgetter("ain"))
    print(row.ain, row.Description)

or even

for row in sorted(
        map(operator.attrgetter("ain", "Description"), adc.cfg.values())):

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