[PYTHON MATRIX-SIG] RubberIndex

[Chris Chase S1A]

I made a suggestion about having array indexing generate an error when
too few indexes are used.  Konrad felt that the analogy to lists was
more important:

>>>>> "Konrad" == Konrad HINSEN <hinsenk@ere.umontreal.ca> writes:

Konrad> That wasn't my point either. My point is that since arrays and nested
Konrad> lists are treated as interchangeable in many situations, it makes
Konrad> sense to use this analogy as much as possible and allow an indexing
Konrad> scheme for arrays that matches that for nested arrays. WHich means
Konrad> that it should always be allowed to have just one index, independent
Konrad> of the rank of the array.


For an array 'a' (rank > 1), the current implementation of a[0] adds
no functionality since it is equivalent to a[0,...].

I would like to make another suggestion along the lines my original
one that also handles the purpose of ravel() for both assignment and
selection.

In IDL, Tela and Yorick using a single index or slice defaults to
indexing an array in flattened form.  Otherwise, the number of actual
indexes used must equal the rank.

A similar implementation could be supported for the array object.
This obviates 'flat' attribute that I suggested earlier.

a[i] indexes 'a' in flattened form.  'i' can be a scalar or a slice.  Then,

a[:] == ravel(a)

and assignment to 'a' in flattened form would also be supported:

a[i] = 2

which eliminates the need for a "flattened" assignment function or for
ravel().

Like other array languages, if more than one index is used without a
rubber index and there are fewer indexes than the array rank then an
error should result.

If 'a' has rank 3, then

a[0] = 1
b = a[0,...]
b = a[0,0,0]

would be valid.  But a[0,0] would generate an error.  This would be
consistent with the fact that a[0,0,0,0] also generates an error.

This implementation still allows an array to be used anywhere where a
sequence object (e.g. list) is used.  

Chris

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