[Python-Dev] PEP 455: TransformDict (original) (raw)

Steven D'Aprano steve at pearwood.info
Sat Sep 14 05🔞12 CEST 2013

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.getcanonical(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:

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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