[Tutor] Reversed dictionary returned by default

[Prasad, Ramit]

Dave Angel wrote:
> On 03/01/2013 02:48 PM, Huperetes wrote:
> > I am getting the following for my installation.
> >
> > Why is this happening, and how do I get it to work properly (returning
> > element 0 - n, versus n - 0)?
> >
> > Python 2.7.3 (default, Apr 10 2012, 23:24:47) [MSC v.1500 64 bit (AMD64)]
> > on win32
> > Type "help", "copyright", "credits" or "license" for more information.
> >
> >>>> params = {"server":"mpilgrim", "database":"master", "uid":"sa",
> > "pwd":"secret"}
> >>>> ["%s=%s" % (k, v) for k, v in params.items()]
> >
> > ['pwd=secret', 'database=master', 'uid=sa', 'server=mpilgrim']
> >
> >>>> ";".join(["%s=%s" % (k, v) for k, v in params.items()])
> >
> > 'pwd=secret;database=master;uid=sa;server=mpilgrim'
> >
> >>>>
> >
> 
> A dict has by specification no specific ordering.  If you want the data
> sorted, then sort the data after extracting it.  Or use some other type.
> 
>  >>>> ["%s=%s" % (k, v) for k, v in sorted(params.items())]
> 
> the only ordering guarantee that you get from dict is that if you
> iterate over it twice with no changes to the dict in the meantime,
> you'll get the same ordering.  But what that ordering is, is undefined.
>   It's certainly not the order that things were entered into the dict.
> 
> 

In Python 2.7+, OP can also try using an OrderedDict[0]. 

"When iterating over an ordered dictionary, the items are returned in the 
order their keys were first added."

Note, that updating a key will NOT change the order, so you must remove 
the key/value pair and then re-add it to change the ordering.


Ramit

[0] http://docs.python.org/2/library/collections.html#collections.OrderedDict


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