[Tutor] is this use or abuse of __getitem__ ?
fomcl at yahoo.com
Mon Sep 17 09:42:41 CEST 2012
I looked at the website and it looks like a cool module. Some of it appeared to be *nix only, but I'll have to dig into it more.
But it's also just like you said: how far should one go with micromanaging things? Maybe some things are the caller's responsibility.
> If you're also supporting the iterator protocol with the __iter__
> method, then I think a helper _items(start, stop, step) generator
> function would be a good idea.
> Here's an updated example (not tested however; it's just a suggestion):
> import operator
> def _items(self, start=0, stop=None, step=1):
> if stop is None:
> stop = self.nCases
> for i in range(start, stop, step):
> retcode1 = self.iomodule.SeekNextCase(self.fh, ctypes.c_long(i))
> self.caseBuffer, self.caseBufferPtr = self.getCaseBuffer()
> retcode2 = self.iomodule.WholeCaseIn(self.fh, self.caseBufferPtr)
> record = struct.unpack(self.structFmt, self.caseBuffer.raw)
> if any([retcode1, retcode2]):
> raise RuntimeError("Error retrieving record %d [%s,
> %s]" %
> (i, retcodes[retcode1], retcodes[retcode2]))
> yield record
> def __iter__(self):
> return self._items()
> def __getitem__(self, key):
> is_slice = isinstance(key, slice)
> if is_slice:
> start, stop, step = key.indices(self.nCases)
> key = operator.index(key)
> start = key + self.nCases if key < 0 else key
> if not 0 <= start < self.nCases:
> raise IndexError
> stop = start + 1
> step = 1
> records = self._items(start, stop, step)
> if is_slice:
> return list(records)
> return next(records)
Awesome, thank you so much. This has been very inspiring! When this is working, I'm thinking about also implementing an Ellipsis (just because it's possible ;-), so I can cut out certain parts of the data using a numpy array. Another idea would be to also use __getitem__ as a dictionary. So when the data contains an id (let's say ssn), r = Reader(key="ssn"); r.data["87654321"] returns the corresponding (first available) record. But although this is cool from an educational perspective, I do wonder whether, from a design perspective, it's a good idea to make __getitem__ this fully packed.
More information about the Tutor