On Thu, Sep 13, 2012 at 9:01 AM, Travis Oliphant
<travis@continuum.io> wrote:
On Sep 13, 2012, at 8:40 AM, Nathaniel Smith wrote:
> On Thu, Sep 13, 2012 at 11:12 AM, Matthew Brett <
matthew.brett@gmail.com> wrote:
>> Hi,
>>
>> While writing some tests for np.concatenate, I ran foul of this code:
>>
>> if (axis >= NPY_MAXDIMS) {
>> ret = PyArray_ConcatenateFlattenedArrays(narrays, arrays, NPY_CORDER);
>> }
>> else {
>> ret = PyArray_ConcatenateArrays(narrays, arrays, axis);
>> }
>>
>> in multiarraymodule.c
>
> How deeply weird
Heh, I guess "expected" is subjective:
In [23]: np.__version__
Out[23]: '1.6.1'
In [24]: a = zeros((2,2))
In [25]: b = ones((2,3))
In [26]: concatenate((a, b), axis=0) # Expected error.
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
/Users/warren/gitwork/class-material/demo/pytables/<ipython-input-26-7cefb735e507> in <module>()
----> 1 concatenate((a, b), axis=0) # Expected error.
ValueError: array dimensions must agree except for d_0
In [27]: concatenate((a, b), axis=1) # Normal behavior.
Out[27]:
array([[ 0., 0., 1., 1., 1.],
[ 0., 0., 1., 1., 1.]])
In [28]: concatenate((a, b), axis=2) # Cryptic error message.
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
/Users/warren/gitwork/class-material/demo/pytables/<ipython-input-28-0bce84c34ef1> in <module>()
----> 1 concatenate((a, b), axis=2) # Cryptic error message.
ValueError: bad axis1 argument to swapaxes
In [29]: concatenate((a, b), axis=32) # What the... ?
Out[29]: array([ 0., 0., 0., 0., 1., 1., 1., 1., 1., 1.])
I would expect an error, consistent with the behavior when 1 < axis < 32.
Warren
It's how the concatenate Python function manages to handle axis=None to flatten the arrays before concatenation. This has been in NumPy since 1.0 and should not be changed without deprecation warnings which I am -0 on.
Now, it is true that the C-API could have been written differently (I think this is what Mark was trying to encourage) so that there are two C-API functions and they are dispatched separately from the array_concatenate method depending on whether or not a None is passed in. But, the behavior is documented and has been for a long time.
Reference PyArray_AxisConverter (which turns a "None" Python argument into an axis=MAX_DIMS). This is consistent behavior throughout the C-API.
-Travis