On Sat, Sep 14, 2013 at 02:25:42AM +0100, MRAB wrote:
> On 14/09/2013 01:49, Steven D'Aprano wrote:
> >d = TransformDict(...)
> >for key in data:
> > key = d.get_canonical(key)
> > value = d[key]
> > print("{}: {}".format(key, value))
> >
> I think must be missing something. I thought that iterating over the
> dict would yield the original keys, so if you wanted the original key
> and value you would write:
>
> for key, value in data.items():
> print("{}: {}".format(key, value))
You're missing that I'm not iterating over the entire dict, just some
subset ("data") that I got from elsewhere. In real code, of course I
would have to handle missing keys. My gut feeling is that normally I
would want both the canonical key and the value, not just any valid key:
# not this
for key in data:
value = d[key]
print("{}: {}".format(key, value))
# but this
for key in data:
key, value = d.getitem(key)
print("{}: {}".format(key, value))
but that's just a gut feeling, and I daresay that it would depend on the
application.
> and if you wanted the transformed key you would apply the transform
> function to the key.
The caller may not know or care what the transformation function is. The
caller may only care about one or two things:
- does this key match a key in the dict?
- what is the canonical version of this key?
For example, in a case-preserving file system, the canonical version of
a file name is whatever the user first typed when they created the file:
create file "SoMe FiLe"
so the canonical version is, "SoMe FiLe". But any of these may be
expected to match:
some file
SOME FILE
Some File
some%20file
etc. It is *not* simply the case that the canonical version is "some
file". Certainly that's not how case-preserving file systems work.
--
Steven
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