[NumPy-Tickets] [NumPy] #1934: Improve assignment error message when output can broadcast to the input

[NumPy Trac]

#1934: Improve assignment error message when output can broadcast to the input
-------------------------+--------------------------------------------------
 Reporter:  mwiebe       |       Owner:  somebody
     Type:  enhancement  |      Status:  new     
 Priority:  normal       |   Milestone:  2.0.0   
Component:  Other        |     Version:  1.6.0   
 Keywords:               |  
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 The code

 {{{
 a = numpy.zeros((5,5))
 v = numpy.ones((5,1))
 a[:,3] = v
 }}}

 raises the exception

 {{{
 ValueError?: output operand requires a reduction, but reduction is not
 enabled
 }}}

 which is not very enlightening as to the nature of the error. This
 illustrates why it errors:

 {{{
 >>> a = numpy.zeros((5,5))
 >>> v = numpy.ones((5,1))
 >>> a[:,3]
 array([ 0.,  0.,  0.,  0.,  0.])
 >>> v
 array([[ 1.],
        [ 1.],
        [ 1.],
        [ 1.],
        [ 1.]])
 >>> a[:,3].shape
 (5,)
 >>> v.shape
 (5, 1)
 }}}

 The (5,) and (5,1) get broadcast to a (5,5) shape, which is what is really
 then being assigned into the (5,) array. To fix it, write the assignment
 like a[:,3] = v[:,0].

 Example taken from ticket #1870 comments.

-- 
Ticket URL: <http://projects.scipy.org/numpy/ticket/1934>
NumPy <http://projects.scipy.org/numpy>
My example project