[Numpy-discussion] Tuples vs. lists when defining recarrays with array()

Robert Kern robert.kern@gmail....
Sun Jun 7 22:15:42 CDT 2009


On Sun, Jun 7, 2009 at 20:44, Fernando Perez<fperez.net@gmail.com> wrote:
> On Sun, Jun 7, 2009 at 4:31 PM, David Warde-Farley<dwf@cs.toronto.edu> wrote:
>> A question was raised on the #scipy IRC earlier today, about the
>> behaviour of array() with structured dtypes. After some educated
>> guessing I figured out that for record arrays, tuples (rather than
>> lists) must be used to indicate atomic elements. What I wondered is
>> whether this behaviour is documented anywhere, and does it belong in
>> the array() docstring, for example? The docstring currently reads "...
>> or any (nested) sequence."
>
> +1 for a clear indication of  this fact, as it's rather unusual that a
> tuple is OK where a list is not (for typical pythyon APIs) and the
> error is *very* obscure.  I've been bitten enough times by this that
> by now I'm used to it, but I distinctly remember much head scratching
> and looking in the wrong places the first time I was hit by this
> behavior.
>
> I don't know if there's a good reason why lists aren't accepted
> though, so that instead of  documenting an oddity it could just be
> cleaned up.  Is it not possible for the constructor to duck-type here
> a list for a tuple?

It may be *possible*, but it's certainly easier this way, and that is
the reason for it.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco


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