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[Python-ideas] OrderedDict literals

Anthony Towns aj at erisian.com.au
Wed Mar 19 01:54:54 CET 2014 
Hi,

I was re-reading some old threads about ordereddict literals to see if
any of them had gotten anywhere. Amongst them, I came across a post by
Tim Delaney:

  https://mail.python.org/pipermail/python-ideas/2011-January/009049.html

that mentioned an odict literal of ['key': 'value', 'key2': 'value2']
could be confused with slice notation.

>From a syntax point-of-view, that doesn't seem to be true (as
mentioned in some of the replies to that thread), but it seems like
you can abuse the similarity to make it a little easier to declare
ordereddicts:

from collections import OrderedDict
class ODSlicer(object):
    def __getitem__(self, key):
        if type(key) is slice:
            key = [key]
        od = OrderedDict()
        for k in key:
            if type(k) is slice:
                od[k.start] = k.stop
            else:
                od[k] = k
        return od
od = ODSlicer()

print(od[1:2])
print(od["a":"b", "c":5])
print(od['a':'b', 'c':'d', ..., 'a':10, 'e':'f'])


You could then replace:

mydict = {
   'foo':    'bar',
   'baz':   'quux',
}

with:

mydict = od[
   'foo':    'bar',
   'baz':   'quux',
]

if you need to convert a hardcoded dict into a hardcoded ordereddict.
Works fine in python2.7 and python3.4.


At this point, I'd like to note in my defence that this isn't called
the python-good-ideas list :)

What's the actual objection to supporting ['foo': 'bar'] odict
literals? I saw Guido gave a -100, way back in the day, but no actual
explanation for why it was distasteful?

    https://mail.python.org/pipermail/python-ideas/2009-June/004924.html

Cheers,
aj

-- 
Anthony Towns <aj at erisian.com.au>
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