[EMAIL PROTECTED] wrote:
> I am wondering if there is a dictionary data type that allows me to
> define the order of access when iterating it using items/keys etc. ?
>
> An example:
>
> a=dict(a=dict(), c=dict(), h=dict())
> prefer=['e','h', 'a']
>
> for x in a.values: print x
>
> would give me
> {h:dict()}, {a:dict()}, then the rest which I don't care about the
> order ?
a straight-forward implementation should be pretty efficient:
for k in prefer:
try:
v = d.pop(k)
except KeyError:
pass
else:
... deal with k, v ...
for k, v in d.iteritems():
... deal with k, v ...
or, non-destructive:
for k in prefer:
try:
v = d[k]
except KeyError:
pass
else:
... deal with k, v ...
for k, v in d.iteritems():
if k not in prefer:
... deal with k, v ...
the latter is trivial to convert into a helper generator:
def ordered_items(d, prefer):
for k in prefer:
try:
v = d[k]
except KeyError:
pass
else:
yield k, v
for k, v in d.iteritems():
if k not in prefer:
yield k, v
for k, v in ordered_items(d, prefer):
... deal with k, v ...
if you insist on having this behaviour in a type rather than a helper,
subclass dict and add ordered_items as a method.
</F>
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