[Numpy-discussion] Syntax Improvement for Array Transpose

[Eric Wieser]

This might be contentious, but I wonder if, with a long enough deprecation
cycle, we can change the meaning of .T. That would look like:

* Emit a future warning on `more_than_2d.T` with a message like "in future
.T will transpose just the last two dimensions, not all dimensions. Use
are.transpose() if transposing all {n} dimensions is deliberate"
* Wait 5 releases or so, see how many matches Google / GitHub has for this
warning.
* If the impact is minimal, change .T
* If the impact is large, change to a deprecation warning

An argument for this approach: a good amount of code I've seen in the wild
already assumes T is a 2d transpose, and as a result does not work
correctly when called with stacks of arrays. Changing T might fix this
broken code automatically.

If the change would be too intrusive, then keeping the deprecation warning
at least prevents new users deliberately using .T for >2d transposes, which
is possibly valuable for readers.

Eric


On Sun, Jun 23, 2019, 12:05 Stewart Clelland <stewartclelland at gmail.com>
wrote:

> Hi All,
>
> Based on discussion with Marten on github
> <https://github.com/numpy/numpy/issues/13797>, I have a couple of
> suggestions on syntax improvements on array transpose operations.
>
> First, introducing a shorthand for the Hermitian Transpose operator. I
> thought "A.HT" might be a viable candidate.
>
> Second, the adding an array method that operates like a normal transpose.
> To my understanding,
> "A.tranpose()" currently inverts the usual order of all dimensions. This
> may be useful in some applications involving tensors, but is not what I
> would usually assume a transpose on a multi-dimensional array would entail.
> I suggest a syntax of "A.MT" to indicate a transpose of the last two
> dimensions by default, maybe with optional arguments (i,j) to indicate
> which two dimensions to transpose.
>
> I'm new to this mailing list format, hopefully I'm doing this right :)
>
> Thanks,
> Stew
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