[Numpy-discussion] Re: Ransom Proposals

Travis Oliphant oliphant at ee.byu.edu
Mon Mar 27 16:37:01 CST 2006


Robert Kern wrote:

>Travis Oliphant wrote:
>  
>
>>Tim Hochberg wrote:
>>
>>    
>>
>>>>Charles R Harris wrote:
>>>>
>>>>    >>> l = list(a)
>>>>    >>> l
>>>>   [999, 1, 2, 3, 4, 5, 6, 7, 8]
>>>>    >>> a
>>>>   array([999,   1,   2,   3,   4,   5,   6,   7,   8])
>>>>    >>> l += a
>>>>    >>> l
>>>>   array([1998,    2,    4,    6,    8,   10,   12,   14,   16])
>>>>    >>> a
>>>>   array([999,   1,   2,   3,   4,   5,   6,   7,   8])
>>>>        
>>>>
>>>Let me add that I think that this is pretty dubious, so if this is a
>>>new feature, perhaps we should revert it before it becomes entrenched.
>>>      
>>>
>>I don't think it's a new feature, but it's simply the result of
>>
>>l += a being translated to
>>
>>l = l + a  # lists don't have in-place add's
>>
>>Numeric has this behavior as well.
>>    
>>
>
>Lists do have in-place adds.
>
>In [1]: a = range(10)
>
>In [2]: b = range(10, 20)
>
>In [3]: id(a)
>Out[3]: 92350264
>
>In [4]: a += b
>
>In [5]: id(a)
>Out[5]: 92350264
>
>In [6]: a
>Out[6]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>
>  
>

True, true.  So, why this behavior?  This seems like a Python issue. 

Compare

a = range(10)
b = arange(10,20)

a.__iadd__(b)

with

a += b


Shouldn't these be equivalent? 


-Travis







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