[Numpy-discussion] advanced indexing question

David Kershaw dskgair at gmail.com
Wed Feb 4 02:22:48 EST 2015


The numpy reference manual, array objects/indexing/advance indexing, 
says: 
Advanced indexing always returns a copy of the data (contrast with 
basic slicing that returns a view).

If I run the following code:
 import numpy as np
 d=range[2]
 x=np.arange(36).reshape(3,2,3,2)
 y=x[:,d,:,d]
 y+=1
 print x
 x[:,d,:,d]+=1
 print x
then the first print x shows that x is unchanged as it should be since y 
was a copy, not a view, but the second print x shows that all the elements 
of x with 1st index = 3rd index are now 1 bigger. Why did the left side of
 x[:,d,:,d]+=1
act like a view and not a copy?

Thanks,
David




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