[Tutor] is this use or abuse of __getitem__ ?
steve at pearwood.info
Fri Sep 14 17:33:11 CEST 2012
On 14/09/12 22:16, Albert-Jan Roskam wrote:
> I defined a __getitem__ special method in a class that reads a binary data
> file using a C library. The docstring should clarify the purpose of the
>method. This works exactly as I intended it, however, the "key" argument is
> actually used as an index (it also raises an IndexError when<key> is
>greater than the number of records in the file). Am I abusing the __getitem__
>method, or is this just a creative way of using it?
No, that's exactly what __getitem__ is for. It does double-duty for key-lookup
in mappings (dict[key]) and index-lookup in sequences (list[index]).
You can also support ranges of indexes by accepting a slice argument.
Another comment below:
> # Python 2.6.4 (r264:75708, Oct 26 2009, 08:23:19) [MSC v.1500 32 bit (Intel)] on win32
> def __getitem__(self, key):
> """ This function reports the record of case number<key>.
> For example: firstRecord = FileReader(fileName) """
> if not isinstance(key, (int, float)):
> raise TypeError
Floats? Do you actually have have case number (for example)
For this case, I think it is reasonable to insist on exactly an int,
and nothing else (except possibly a slice object, to support for
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