dictionary issue (and maybe PEP ... depending on the answer)
staschuk at telusplanet.net
Mon Jun 2 09:03:21 CEST 2003
> >>> [_months[i] for i in _months.keys()]
> The issue is, this consistently returns the months in order. [...]
Heh. Normally we get people complaining about dicts *not*
providing items in order.
> [...] I don't see
> any obvious reason that it does, but I can't get it to fail. So,I am
> wondering if there is a reason, or is it serendipity.
Perhaps the following previous post of mine will make clear why it
happens with this data:
I'd discourage you from relying on this in your code, and
especially from relying on it implicitly. Something like
months = [(1, 'January'),
monthdict = dict(months)
monthnames = [name for number, name in months]
also guarantees the ordering of monthnames, but makes that
guarantee not only resistant to any future change of the dict
implementation, but also clear to the reader.
> Assuming that there is not a good reason, the PEP idea is adding a
> sorted_keys() method to dictionaries which would just return the keys in
> the same order they would be in by doing this.
> >>> l = d.keys()
> >>> l.sort()
> The advantage is that using dictionary keys in list comprehensions would
> be easier, but other than that it is not too big a deal.
I'd be -1 on this, fwiw. It's rarely needed in my experience;
when order really does matter, I'd use a list anyway; if I really
need a dict and don't want to use a list, writing
L = list(iterable)
and asking for
is just as easy. And it's just one more thing for dict-like
objects to implement.
Steven Taschuk staschuk at telusplanet.net
"Its force is immeasurable. Even Computer cannot determine it."
-- _Space: 1999_ episode "Black Sun"
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