[Numpy-discussion] Object array from list in 1.6.0 (vs. 1.5.1)

Ken Basye kbasye1@jhu....
Fri Jun 10 11:40:55 CDT 2011

Dear folks,
   I have some code that stopped working with 1.6.0 and I'm wondering if 
there's a better way to replace it than what I came up with.  Here's a 
condensed version:

x = [()]  # list containing an empty tuple; this isn't the only case, 
but it's one that must be handled correctly
y = np.empty(len(x), dtype=object)
y[:] = x[:]

In 1.5.1 this works, giving y as "array([()], dtype=object)"

In 1.6.0, it raises a ValueError:
ValueError: output operand requires a reduction, but reduction is not 

I didn't see anything in the release notes about this; admittedly it's a 
very small corner case.   I also don't understand what the error message 
is trying to tell me here.

Most of the more straightforward ways to construct the desired array 
don't work because the interpretation of a nested structure is as a 
multi-dimensional array, which is reasonable.

At this point my workaround is to replace the assignment with a loop:

for i, v in enumerate(x):
      y[i] = v

but this seems non-Numpyish.  Any light on what the error means or a 
better way to do this would be most welcome.


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